Infection: Definition, Causes, Symptoms, Categories, and Impact

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- Updated by Sarah Qaiser
Medically reviewed by Dr Sidra Samad



An infection is the result of the invasion and growth of germs in the body, which cause illness in the affected person. There are five main ways that an infectious agent enters the body: inhalation, ingestion, direct contact, physical contact with infected matter, contact with objects carrying infection and the chain of infection. There are seven key symptoms of infection which follow contamination: coughing and sneezing, fever, vomiting, inflammation, diarrhoea, fatigue and cramps. There are five types of infectious agents responsible for these symptoms: viruses, bacteria, fungi, protozoa and helminths. 

The time it takes for an infection to impact the body depends on the type of infection. However, there are four phases which happen after any infectious agent invades a host: incubation, prodromal, acute and convalescence.  In the second phase, prodromal, the pathogen starts to reproduce and bodily symptoms intensify. The symptoms at this stage can be non-specific to a certain infection, or can clearly indicate a particular disease. The point at which an infection most affects the body is the acute phase, wherein the infectious agent multiplies rapidly causing pronounced symptoms and peak immune system response. 

What is an Infection?

An infection is the result of the invasion and growth of germs in the body. The host tissues react to the infectious agent and the toxins they produce, which results in an infection in the body. Any infected person can transmit the infection, regardless of if they are sick with symptoms or if they are colonised with germs but not presenting with any symptoms. The severity of an infection can range from mild to fatal.

There are three requirements for an infection to develop: a source, a susceptible person and transmission. The source refers to where the infectious agents, such as gems, viruses, bacteria or other microbes live, which can be on a surface or on human skin. The susceptible person refers to the way the germs enter the body. The transmission refers to the movement of germs to the susceptible person. 

What is the Medical Terminology of Infection?

In the field of medicine, an infection is defined as the entrance and development of an infectious agent in a human or animal body. The medical terminology used to describe the process of infection is the invasion and multiplication of harmful microorganisms that are not normally present within the body. The microorganisms are problematic because they either invade body tissues or release toxins. The type and severity of the infection inform the treatment which will be recommended to treat it. 

When does an Infection Occurs?

An infection occurs when germs enter the body, multiply in number, and cause a reaction in the host. There are three requirements for an infection to successfully develop: a source, a susceptible person and transmission. 

What are the Causes of Infection?

There are five main ways that an infectious agent enters the body: inhalation, ingestion, direct contact, physical contact with infected matter, contact with objects carrying infection and the chain of infection. 

  • Inhalation. One way that an infectious agent enters the body is by the person breathing in airborne bacteria from coughs and sneezes. 
  • Ingestion. The susceptible person may consume something which has been contaminated with the bacteria, such as food or poorly sanitised water.
  • Direct contact. An infective agent can enter the body via direct contact with the body, such as in breaks in skin resulting from injury, skin conditions or bites that breach the skin barrier. 
  • Physical contact with infected matter. If a person comes into contact with infected matter from wounds or bodily fluids then it is very likely that they too will become infected.
  • Contact with objects carrying infection. The medical terminology to describe contacts carrying infection is fomites. Fomites are capable of transmitting organisms from one individual to another. Some key examples of fomites are clothing, brushes, towels and linens.  
  • The chain of infection. The chain of infection describes how microorganisms are transmitted from one person or place to another. The chain of infection consists of six stages. First, the infectious agent refers to the microorganism which causes the infection. Second, the reservoir refers to where the germ lives and grows. Third, the portal of exit refers to the way out of the infected person that the germ takes. The portal of exit depends on the type of infection, severity of illness and the symptoms that the person is presenting with. Fourth, the mode of transmission refers to the way in which the germ is spread from one person to the next. Fifth, the portal of entry refers to the way in which the germ enters the next person. Sixth, the susceptible host refers to the vulnerable person who is at risk of infection because they are unable to fight the infection. An example of a susceptible host is an elderly person living in a care home, as their population already has decreased immune systems as well as many residents living closely together. 

  • What are the Symptoms of Infection?

    There are seven key symptoms of infection: coughing and sneezing, fever, vomiting, inflammation, diarrhoea, fatigue and cramps. 

    1. Coughing and Sneezing

    Coughing and sneezing are two prominent symptoms of infection. Coughing and sneezing protect the lungs and throat from bacteria and viruses. There are two main types of cough: productive and non-productive. A productive cough serves to expel mucus from your airways, whereas a non-productive cough doesn’t have a specific function. There are three different types of sneeze, which typically occur in succession. The first sneeze breaks up the irritant causing nasal discomfort, the second sneeze brings the debris into the nostrils and the third expels it from the nose. Coughing and sneezing are both symptoms of an infection because they demonstrate that the body is trying to get rid of unwanted particles. 

    There are a handful of side effects which can occur after extended periods of coughing or sneezing. Extended periods of coughing can cause irritation to the lungs, which prolongs the symptom. Persistent coughing can also cause sleeplessness due to the sufferer not being able to sleep for a sufficient number of hours, urinary incontinence due to the stress on the bladder and even vomiting because the muscles used in the cough reflex are the same muscles which are responsible for vomiting. It is very uncommon for sneezing to cause any serious adverse effects. It is possible for an extended period of sneezing to cause excess tension and damage in the vocal folds, which can impact the sufferer’s voice. In an incredibly rare number of cases, sneezing forcefully can cause laryngeal fractures. There is a very low risk of laryngeal fractures which occur as a result of sneezing. 

    2. Fever

    A high fever is a recognisable symptom of infection. A fever is a rise in body temperature that forms part of the body’s overall immune system response to the infection. There is only cause for concern when the sufferer's temperature reaches more than 38 degrees celsius when measured with a thermometer.  When the body is fighting an infection, it produces additional white blood cells to fight the bacteria, virus, or other foreign substance. The increase in white blood cells affects the hypothalamus, which is the region in the brain that controls body temperature. A fever is a symptom of infection because it indicates that the hypothalamus is being affected by the increase in white blood cells being produced to fight the illness. 

    Depending on the severity of the fever, the sufferer may also present with chills, headache, muscle aches, loss of appetite and general weakness. Generally, the fever will subside in a few days without treatment. There are three instances in which you should seek medical attention. You should call 111 or your GP surgery if the high temperature lasts for five or more days. If the fever is causing significant discomfort, with regards to irritability, vomiting, headache or any cluster of side effects, then you should seek medical attention. If the sufferer has any immune system problems or preexisting illness, then it is advisable to consult a doctor as soon as they present with any fever.

    3. Vomiting

    Vomiting is a general symptom of bacterial infection. The location and type of bacteria that is causing the symptoms can vary. Vomiting is most commonly associated with the 'stomach flu', unrelated to the respiratory flu, the actual name for which is gastroenteritis. Gastroenteritis is an infection caused by one of three viruses: rotavirus, norovirus and adenovirus. It causes the lining of the gastrointestinal tract to become inflamed, which can lead to pain, nausea and vomiting. Alternatively, if the vomiting is accompanied by dizziness and vertigo, then it may be caused by an inner ear infection. 

    Vomiting is a symptom of infection because it serves as the body's attempt to prevent any harmful substance or irritant from travelling further around the body. Vomiting is a natural response, as the body assumes the sufferer has consumed something poisonous and expels the contents of the stomach in order to protect the rest of the body.  

    There are three main side effects of vomiting which occur over an extended period of time. First, the sufferer can become severely dehydrated due to the amount of water they are losing at a fast rate. Second, the stomach acid in vomit can damage the oesophagus as it travels from the stomach to the mouth. Repeated vomiting can damage the gastrointestinal tract due to  repeated exposure to stomach acid. Third, the stomach acid in vomit can also cause damage to the sufferer's teeth. The stomach acid corrodes tooth enamel, which leads to decay. 

    There are two cases in which you should seek medical attention for vomiting. First, it should be noted that vomiting usually lessens within 6 to 24 hours. Should it continue beyond this timeframe, then you should seek medical attention. Second, if a head injury is suspected to have caused the vomiting, then you should seek medical attention immediately. 

    4. Inflammation

    Inflammation is a visible symptom of infection. Inflammation refers to the increased blood flow to the affected area, causing redness and warmth. Inflammation manifests as redness, soreness and swelling, as well as pain and bruising. The physical swelling is caused by an increased number of white blood cells flowing to the area. 

    Inflammation is a symptom of infection because it is the body's attempt to isolate and contain the bacteria. Inflammatory cells respond to infection by trapping the irritant, halting its progress, and initiating the healing process of affected tissue. Inflammation is a defence mechanism, whereby the immune system responds to pathogens (bacteria or viruses) which cause infection by isolating them and bringing white blood cells to the affected area.

    Inflammation only provides cause for medical concern if it doesn't subside after a few days. There are two types of inflammation: acute and chronic. Acute inflammation is the immediate protective response to infection, lasting only a few days. Chronic inflammation occurs when the infection doesn't go away, by virtue of not being treated or resisting any attempted medical interventions. Chronic inflammation is problematic because it can lead to the attack of healthy tissues and organs. Chronic inflammation leads to an increase in inflammatory cytokines. Cytokines are the cells which stimulate inflammation. If there is an overproduction of cytokines, then the inflammatory response may become misguided and begin to target healthy joint and muscle tissue. Chronic inflammation is associated with heart disease, diabetes, cancer, arthritis, and bowel diseases.

    5. Diarrhoea

    Diarrhoea is another symptom of infection which is most commonly caused by gastroenteritis. Bacteria can enter the body via contaminated food or water and cause food poisoning. Bacteria such as campylobacter, Clostridium difficile (C. difficile), Escherichia coli (E. coli), salmonella or shigella all cause food poisoning,  which results in diarrhoea. However, most cases of diarrhoea are caused by viruses. In cases of diarrhoea caused by a virus, it's likely that the sufferer will also experience cramping, nausea, loss of control of bowel movements and pain in the abdomen.

    Diarrhoea is a symptom of infection because it is the body's way of quickly clearing viruses, bacteria or toxins from the digestive tract. diarrhoea plays a crucial role in the clearing of bacteria which is found in intestines at the beginning of an infection. 

    The most dangerous component of diarrhoea is how long the symptom lasts. Diarrhoea can safely last anywhere between a couple of days and two weeks, depending on the severity of the symptom. If the diarrhoea lasts longer than a few days then it could be a sign of a more serious health condition that requires further attention. If the diarrhoea is severe and lasting more than two days, then the sufferer could become fatally dehydrated. There are three situations in which you should seek immediate medical attention. First, if the sufferer cannot keep any water or food down. Second, if the stool they are expelling contains blood. Third, if the sufferer is presenting with a very high fever alongside diarrhoea.

    6. Fatigue

    Fatigue refers to a feeling of constant tiredness or weakness, which is not alleviated by rest or sleep. It is a general symptom of bacterial infection. Fatigue can be mental, physical or a combination of both. Fatigue is typically accompanied by other symptoms like fever, headache, shortness of breath or appetite loss. Infections that can cause fatigue are flu, covid, hepatitis, HIV and pneumonia. 

    Fatigue is a symptom of infection because the body becomes lethargic from fighting illness. Fatigue is one part of the body's response to fighting an infection, as the body is calling the sufferer to sleep as an essential component of recovery. 

    Fatigue is a natural part of the body's response to infection. However, if the sense of tiredness and weakness lingers beyond the period of infection, then it can progress to post-viral fatigue. Post-viral fatigue can disrupt everyday activities, and the sufferer's ability to maintain their work, school and social responsibilities. Extended post-viral fatigue can necessitate extensive lifestyle changes, which can impact the sufferer's mental and emotional health. 

    7. Cramps

    Cramps are a sudden and involuntary contraction of an entire muscle group, individual single muscle or select fibres. A bulging lump of muscle tissue at the area of infection is common. Three examples of infections which can cause cramps are urinary tract infection (UTI), gastroenteritis and kidney infection. First, UTI is often accompanied by pelvic and lower back cramps. Second, gastroenteritis is often accompanied by abdominal cramping. Third, the first signs of a kidney infection are often cramps in the sufferer's side or lower back. It should be noted that a cramp limited to a specific area does not necessarily mean the cause of the cramp is local. If sustained over an extended period of time, cramps can interfere with daily activities. The sufferer's quality of sleep can be affected if the cramps repeatedly occur at night. Cramps present a very low risk to quality of life, unless the condition becomes chronic.

    What are the Risk Factors of Infection?

    There are four main risk factors of infection: low white blood cell count, immunosuppressant medications, certain types of cancers and certain medical conditions. 

  • Low white blood cell count. If the person has a relatively lower number of white blood cells, then they are at more risk of infection because their immune system is compromised and therefore less able to fight infection. Cancer treatments, such as chemotherapy, radiation, stem cell transplants, and bone marrow transplants, can cause a reduced white blood cell count. 
  • Immunosuppressant medications. Some medications, such as steroids, are designed to slow or stop the response of the immune system. In a healthy body, the immune system helps to fight off infections that cause illness. A symptom of some medical conditions is that the immune system cannot distinguish between helpful and harmful cells, so it attacks the body’s own tissues as if they were germs. Immunosuppressant medications can stop or at least slow this response, in order to mitigate cell damage, inflammation and other symptoms. People who take immunosuppressant medications in order to combat their autoimmune disease are more at risk of infection, as their immune system is compromised. 
  • Certain types of cancers. Some cancers, such as those which affect the bone or bone marrow, can increase the person’s risk of infection. 
  • Certain medical conditions. Similarly to certain types of cancers, there are certain medical conditions which make someone more vulnerable to infection. Some conditions which can weaken the immune system, and increase the person’s risk of infection, are diabetes, alcoholism, HIV/AIDS, rheumatic or congenital heart disease, asthma or other chronic lung diseases.

  • What are the major Categories of Infectious Agents?

    There are five major categories of infectious agents: viruses, bacteria, fungi, protozoa and helminths. 

    1. Viruses

    Viruses are non-living infectious agents which require host cells. Viruses are genomes encased in a protein coat, called a capsid. The capsid is sometimes covered by an additional layer of lipids, known as an envelope. Viruses cannot replicate on their own, so they use the protein synthesis pathways of their host cell. The process of virus replication is as follows: the virus first inserts its genetic material into the host cell, then exploits its proteins to reproduce, before the cell is burst by the large amount of viral replicates produced. This process always damages, and often kills, the host cell. Some viruses can insert themselves into the host cell and remain there for several months or years, before re-appearing later in the host’s life. 

    Viruses cause symptoms by killing cells or disrupting cell function. The effects of a virus are typically shorter-lived than those of bacteria. Some classic viral symptoms are fever, throat pain, nasal congestion, coughing and body aches. Viruses are responsible for many of the familiar infectious diseases, such as the common cold, flu and warts. However, they are also responsible for severe illnesses like HIV and AIDS, Ebola and Covid-19. Viruses become an infectious agent by hijacking healthy cells. Viruses can attack various cells in the body, such as the liver, respiratory system, or blood. The multiplication of the virus in the host cell leads to the death, damage or otherwise changing of previously healthy cells, which is what makes the sufferer unwell.

    2. Bacteria

    Bacteria are living infectious agents made up of only one cell, the scientific term for which is a unicellular organism. Bacteria have a simple structure made up of a cell wall, containing cytoplasm, bacterial DNA and plasmid DNA, attached to which is the flagellum. The two types of DNA inside the bacterial cell replace the nucleus, the control centre, found in most plant and animal cells.  The flagellum is a collection of tail-like structures, which together enable the bacteria to move through liquids. Unlike viruses, bacteria can live and replicate outside host cells. Infection is either caused by the bacteria reproducing or releasing toxins which damage the body’s cells. 

    Bacteria are not necessarily harmful, but they become an infectious agent by getting into a place in the body where they shouldn’t be. Bacteria are responsible for many infections, such as strep throat, ear infection, urinary tract infection, sinus infection and sexually transmitted infections. Common effects of a bacterial infection are fever, fatigue, headache, nausea and vomiting. Any bacterial infection that gets deep into the body, like in the blood, heart, lungs or brain, can be fatal.

    3. Fungi

    Fungi are living infectious agents made up of hyphae, which are long thread-like structures. The hyphae fit together to form a mesh-like structure, the technical term for which is mycelium. Unlike bacteria, fungi have a nucleus. Fungi can switch between a unicellular form and a multicellular form. Fungi reproduce by releasing spores, cells which can develop into a new cell without needing to come into contact with another reproductive cell, which cause infection by means of direct contact, inhalation or ingestion. 

    Fungi become infectious agents when people breathe or come into contact with the  fungal spores. Infections caused by fungi are more common in people who are already immunocompromised, as healthy individuals are innately highly resistant to fungal infection. Some examples of common fungal infections are ringworm, vaginal yeast infections, and athlete’s foot. The symptoms of fungal infection depend on the location of the afflicted area. For example, fungal infections of the skin typically cause redness, itchiness, flaking and swelling, whereas fungal infection of the lungs causes coughing, fever, chest pain and muscle aches.

    4. Protozoa

    Protozoa are unicellular infectious agents which contain a nucleus that can be mobile or parasitic. Parasitic protozoa are the type which most commonly cause disease in humans. Protozoa can multiply in humans, which means fatal infections can develop from a single organism. There are several different species of protozoa, which are so diverse that they can't be effectively treated with one type of antiprotozoal. Protozoa become an infectious agent by means of faecal-oral contact.The  protozoa that live in a human's intestine can be transmitted to another human by means of contaminated food, water or person-to-person contact. Alternatively, protozoal infection can be transmitted by arthropod vectors. Arthropod vectors are insects which carry and transmit pathogens from one host to another. Examples of arthropod vectors are mosquitoes, flies, biting midges, ticks, mites, fleas, bugs and lice. 

    Like other infectious agents, protozoal infection results in tissue damage that leads to disease. Some examples of illnesses caused by protozoan infection are African sleeping sickness, amoebic dysentery and malaria. Additionally, protozoal infections are among the most common life-threatening secondary infections in patients with HIV.

    5. Helminths

    Helminths are parasitic worms which can range from 15 to 35 centimetres in size. Helminths become infectious agents by producing eggs, whereby each individual egg is capable of producing thousands of new worms. Helminths are visible to the naked eye in their adult stages, but they cannot multiply in humans at this level of maturity. There are three main types of helminth which can cause infection in humans: flatworms, thorny-headed worms and roundworms. 

    Three common infections caused by soil-transmitted helminths are hookworm, ascaris and whipworm. It should be noted that soil-transmitted helminths specifically affect the nutrition of the infected person. The parasites feed on host tissues, including blood, which results in a loss of iron and protein. Hookworm in particular can cause extreme intestinal blood loss which can cause the sufferer to develop anaemia. 

    What are the Complications of Infection?

    Infection can spread from the one area initially affected to the entire body via the bloodstream. If the infection spreads to the entire body, then the person is at risk of three complications: bacteremia, sepsis and septic shock. It should be noted that these are fatal complications which require immediate medical attention. 

    1. Bacteremia. Bacteremia refers to the spread of bacteria to the blood. Bacteria can occur when infections in the lungs, kidney or skin travel to the bloodstream. Bacteremia can also occur when catheters become infected and consequently contaminate the person via the bodily cavity into which they are inserted. 
    2. Sepsis. Sepsis refers to an extreme response of the immune system to an infection. In a typical immune system response, chemicals are released at the affected area to fight off infection. In sepsis, chemicals are released throughout the body. Sepsis is associated with inflammation and clotting, which decrease blood flow and oxygen to organs. If left untreated, sepsis will injure tissues and organs to a life-threatening degree. The Sepsis Alliance promotes the abbreviation ‘TIME’ to help people remember the markers of fatal sepsis. The ‘T’ stands for temperature, whereby the sufferer may have an extreme fever or chills and shivering. The ‘I’ stands for infection, whereby it should be checked whether the sufferer was already presenting with signs or symptoms of an existing infection. The ‘M’ stands for mental decline, whereby the sufferer should be immediately brought to hospital if they become confused, sleepy or difficult to rouse. The ‘E’ stands for extremely ill, whereby the sufferer may show signs of severe pain, discomfort, and shortness of breath. 
    3. Septic shock. Septic shock refers to the progression of untreated sepsis. As the sepsis worsens the sufferer’s blood pressure becomes fatally low, preventing vital organs from getting sufficient blood, depriving them of oxygen. This causes organs to shut down, and can cause permanent damage. Septic shock is treated with medications known as vasopressors, which maintains the person’s blood pressure at such a level that blood is still reaching their organs. 

    How do Infections Propagate?

    As previously established, there are five main ways an infectious agent enters the body: inhalation, ingestion, direct contact, physical contact with infected matter, contact with objects carrying infection and the chain of infection. The mode of transmission of a given infection thus fits into one of the five categories. For example, coughing and sneezing are symptoms of infection. Coughs and sneezes create respiratory droplets which are then inhaled by other people, propagating the infection. 

    What are the Types of Infections?

    There are four main types of infection: viral, bacterial, fungal and parasitic. The four main types of infection are listed below. 

    1. Viral. Viral infections are when the infectious agent hijacks host cells and uses their resources to reproduce, as they cannot multiply alone. Two examples of common viral infections are the flu and coronavirus. 
    2. Bacterial. Bacteria are not necessarily harmful, and there are many types of bacteria which are essential to maintaining bodily functions. However, bacterial infection occurs when the bacteria reaches a part of the body where it is not supposed to be. Bacteria invade the body via an open wound or the airways, and cause sickness by reproducing or releasing toxins which damage the body’s cells.
    3. Fungal. Fungal infections propagate via airborne spores, which cause infection by means of direct contact, inhalation or ingestion. Fungi become infectious agents when people breathe or come into contact with the  fungal spores, and they enter and multiply inside of the body. 
    4. Parasitic. Parasitic infections are caused by helminths. Helminths are parasitic worms which lay eggs, each of which can produce thousands of worms. Helminths enter the body through contaminated substances, most commonly soil, and then reproduce. Three common infections caused by soil-transmitted helminths are hookworm, ascaris and whipworm.
    How to Determine the Types of Infection?

    In order to determine the type of infection in the body, doctors will perform several tests. Bacteria, viruses and fungi can show up in body fluids, such as blood, urine, faeces, spit, cerebrospinal fluid, bone marrow and skin cells. Therefore, a sample of each of these fluids will be taken from the sufferer and tested in a laboratory. The methods of testing used on the fluids are as follows: culturing, using a specialised machine which looks for antibodies in the blood, examining under a microscope and Polymerase Chain Reaction (PCR) testing of genetic material which will expose the presence of viruses.

    What is the Most Common Type of Infection?

    Hepatitis B is the most common type of infection. According to the World Health Organisation (WHO), as of 2019, 296 million people worldwide were infected with the hepatitis B virus. Hepatitis B is considered a major global health problem. 

    Hepatitis B is such a prevalent infection because it can be spread several different ways. First, the infection can spread from mother to child at birth. An infected child can also pass the infection to an uninfected child via horizontal transmission, which refers to exposure to infected blood. Second, Hepatitis B can be spread by needlestick injury, tattooing, piercing if the tools are not properly sanitised. Third, the infection can be transmitted via exposure to infected blood and body fluids, such as saliva and menstrual, vaginal and seminal fluids. Fourth, Hepatitis B can be spread through the reuse of contaminated needles, syringes, and other sharp objects in a formal healthcare setting or in an informal setting amongst a community of people who inject drugs.

    How to Prevent Infection?

    There are several ways to prevent infection. First, keeping good personal hygiene is a reliable way to lessen chances of infection. Infections can be prevented by washing your hands thoroughly with soap after using the restroom, before eating, and after handling a sick pet or person. It is never a good idea to share dishes, glasses, and utensils. As a result, you should refrain from sharing such items with others. Second, sterilise and bandage any cuts or injuries, and consult your GP if you have been bitten by an animal.

    How is an Infection Diagnosed?

    In order to diagnose an infection, a doctor will examine the results of the tests which have been run on your fluid samples. Different infections have different markers which are visible in blood, urine, faeces, spit, cerebrospinal fluid, bone marrow and skin cells. 

    What are the Possible Treatment for Infection?

    Infections can be treated in several ways. The four main treatments for infection are listed below.

      • Antibiotics. Infections caused by bacteria are usually treated with antibiotics, since bacteria are living organisms and can be neutralised by the medicine within antibiotics. Antibiotics are prescribed depending on which strain of bacteria is causing the infection.
      • Antivirals. Antiviral drugs can treat most viral infections, by means of binding to receptors in cells, so viruses cannot penetrate and damage healthy cells.
  • Antifungals. Antifungal medications are generally topical, to be applied to the affected area of skin or nail. If the fungal infection is located in the lungs or organs, then oral or intravenous antifungal medications are available. 
  • Antiparasitic. Antiparasitic drugs are a group of medications used to treat infections caused by parasites, including both protozoa and helminths. Antiparasitic drugs kill the parasites, to the effect of killing the parasite or its eggs, stopping their growth or paralysing them so they cannot attach to the host.
  • How common is Infection?

    According to the Parliamentary Office of Science and Technology, infectious diseases pose a significant health burden in the United Kingdom, accounting for 7% of all deaths. Men, women, children, teens and seniors all have different susceptibilities to infection and the resulting illness. 

    A research article published in 2014 which explored sex differences in parasitic infections found that men are more severely affected by several parasites. The article found that although there are some parasites which more commonly infect women and children, men are more susceptible to be severely affected (Bernin & Lotter, 2014). 

    Women are more susceptible to urinary tract infections and yeast infections, due to the fluctuations in hormone levels during menstruation, pregnancy and menopause which affect the immune system. Additionally, the immune response to foreign bodies in women had to evolve to allow for pregnancy. The female immune system is more ‘plastic’ than that of males, in order to prevent the rejection of a partly “immunologically foreign” foetus. Moreover, the role of women as caretakers and mediators of health for their families increases their risk of exposure to infectious diseases (Gerberding, 2004). Women’s fulfilment of these roles also pose obstacles to adequate and timely treatment should they develop an infectious disease. 

    According to the American Academy of Pediatrics, ear infections are one of the most common childhood illnesses. Children are more prone to ear infections than adults, which can be caused by bacteria or viruses. According to JAMA Pediatrics, 50% of children will have had at least one ear infection by the time they reach two years of age (Paul & Moreno, 2020)

    Although teenagers are exposed to the same germs as the rest of the population, this age group is more susceptible to getting ill from certain germs than other age groups. According to the Center for Disease Control and Prevention, children aged between 5 and 15 are vulnerable to infection by the Streptococcus bacteria that causes strep throat. 

    Infection and infectious diseases pose a serious risk for the senior population. According to the American Academy of Family Physicians, one third of all deaths in people over the age of 65 results from infectious diseases. Pneumonia is cited as the most lethal infection for seniors, due to the reduced lung capacity, increased exposure in care home or assisted living communities and weakened immune system in this population.

    (citations for statistical information formatted in APA style)

    Bernin, H. & Lotter, H. (2014). Sex Bias in the Outcome of Human Tropical Infectious Diseases: Influence of Steroid Hormones. The Journal of Infectious Diseases, 209(3), 107-113.

    Gerberding J. L. (2004). Women and infectious diseases. Emerging infectious diseases, 10(11), 1965–1967.

    Paul, C. R. & Moreno, A. M. (2020). Acute Otitis Media. JAMA Pediatrics, 174(3), 308-308.

    How quickly does an Infection impact the Body? 

    The time it takes for an infection to impact the body depends on the type of infection. For example, after ingesting contaminated food, it can take between 6 and 24 hours for the infection to produce symptoms in the body. The body responds to infection by activating the immune system, which may cause a fever, introducing white blood cells to neutralise and destroy the pathogens. 

    There are four phases which happen after an infectious agent invades a host: incubation, prodromal, acute and convalescence. In the first phase, incubation, the infection causes little to no physical symptoms. In the second phase, prodromal, the pathogen starts to reproduce and bodily symptoms intensify. The symptoms at this stage can be non-specific to a certain infection, or can clearly indicate a particular disease. The point at which an infection most affects the body is the acute phase, wherein the infectious agent multiplies rapidly causing pronounced symptoms and peak immune system response. The fourth phase, convalescence, refers to decrease of bodily symptoms due to the sharp decrease in pathogen numbers after the peak. 

    How quickly does an Infection impact the Brain?

    Sudden onset and chronic infections can cause damage to the brain, such as septicemia, bacterial meningitis and encephalitis. An infection begins to impact the brain anytime between the first hours of contamination and several weeks after, depending on the type of infection. 

    One such infection is septicemia, whereby the bacteria has invaded the bloodstream. Septicemia causes decreased body temperature, sudden drop in blood pressure and blood clotting. If the low blood pressure is left untreated for a prolonged period then the brain can become deprived of blood, and therefore oxygen. This starvation causes permanent damage, the medical terminology for which is hypoxic brain injury. Hypoxia begins to take effect after five minutes of oxygen deprivation, with extended deprivation leading to coma, seizures and brain stem death. 

    Another such infection is bacterial meningitis. Meningitis is an infection of the membranes that protect the spinal cord and brain, which when infected, can become inflamed and press on either structure. Serious brain damage can occur within the first hours of the symptoms being detected, due to the hazardous location of the infection. If left untreated, meningitis can cause seizures, deafness, blindness, neurological damage, speech, behavioural or learning problems, and paralysis.

    Encephalitis is a viral infection which causes irritation and inflammation of the brain. Encephalitis may first present with flu-like symptoms, with increasingly severe symptoms like disorientation and seizures developing in the following hours, days or weeks. It should be noted that encephalitis can also result from bacterial diseases such as syphilis, lyme disease, and tuberculosis. Encephalitis causes clumsiness, drowsiness, confusion, irritability, sensitivity to light, seizures, change in mental state, impaired judgement and memory loss. There are several steps the doctor will take in order to diagnose encephalitis. They may administer brain scans, such as an MRI, head CT or electroencephalogram, or specifically inspect the spine by means of a lumbar puncture (commonly known as a ‘spinal tap’) or a cerebrospinal fluid analysis. 

    How does Nicotinamide Adenine Dinucleotide help for Infection?

    Nicotinamide adenine dinucleotide (NAD) affects both antiviral and anti-inflammatory responses. NAD is essential to regulating essential cellular functions, as it can store and release energy as required by the cell. NAD promotes antiviral and anti-inflammatory responses to infection by facilitating the necessary cellular components in the immune system. 

    How Long Does an Infection Last?

    A viral infection can last anywhere between 3 to 14 days. A bacterial infection can last up to 14 days without treatment, but medical attention should be sought if significant symptoms persist for 10 or more days. 

    Is an Infection Curable?

    Yes, an infection is curable. There are four main treatments for infection: antibiotics, antivirals, antifungals and antiparasitics. Both viral and bacterial infections can be treated with the appropriate medication. 

    Is an Infection Contagious?

    Yes, an infection can be contagious. Contagious refers to an infection that can be spread from person to person. Infectious diseases are spread through the transfer of bacteria, viruses or other germs from one person to another. Infection can spread from person to person through the inhalation of respiratory droplets, faecal-oral contamination, exposure to blood or other bodily fluids and sexual contact. 

    Is an Infection a Disease?

    Yes, an infection is a disease. A disease refers to any deviation from the body’s normal structural or functional state. An infection is the result of the invasion and growth of germs in the body. The host tissues react to the infectious agent and the toxins they produce, which results in an infection in the body. Therefore, an infection is a disease because the body is damaged as a result of an infectious agent entering the body.

    Is Covid an Infection?

    Yes, Covid is an infection. Covid-19, also known as coronavirus, is caused by the SARS-CoV-2 virus.  The Covid virus is spread from person to person by means of large respiratory droplets and smaller aerosols which are expelled from the infected person’s mouth or nose when they breathe, speak, sneeze and cough.

    What is the difference between Viral and Bacterial Infections?

    The primary difference between viral and bacterial infections is that the former is caused by viruses and the latter is caused by bacteria. It should also be noted that antibiotic drugs are effective in killing bacteria but they aren’t effective against viruses.

    What is the difference between Infectious and Contagious?

    The primary difference between infectious and contagious diseases is that the former is spread by germs entering the body but not directly by person to person, and the latter can be spread from one human to another.