Susceptibility to Infection

Constantly sick – is that still normal or a sign of a weak immune system and therefore an increased susceptibility to infections? Here you can find out which symptoms indicate an immune deficiency and what treatment options are available. But it’s not just illnesses that cause a weakened immune system, also certain medications and therapies as well as age, pregnancy and an unhealthy lifestyle.

infection flu

What does “morbidly susceptible to infection” mean?

In medicine, a distinction is made between physiological and pathological susceptibility to infections. The word “physiological” describes how the body normally behaves in healthy people. “Pathological,” on the other hand, refers to the cause, development, structural/functional changes and natural history associated with diseases.

Physiological susceptibility to infections

Babies are born with immature immune systems. The immune defense must first get to know the germs in the environment and develop strategies to combat them – immunity against the pathogen in question then develops. It is therefore completely normal for babies and small children, for example, to feel like they have a cold all the time – or at least significantly more often than adults.

Children usually experience more infectious diseases each year before they reach school age than afterward. In a large-scale older study, children were infected with respiratory diseases on average about five times in the first four years of life. From the age of five onwards, they became ill less often. Experts now assume a maximum of eight mild infections per year. However, there is currently no very current data on how many infectious diseases children normally experience at what age.

The immune system of adults also must repeatedly deal with pathogens that it has not previously come into contact with. That’s why everyone catches a cold, gets athlete’s foot or gets a gastrointestinal infection at least once a year.

Experts refer to this as a physiological susceptibility to infection. In most cases, however, the immune system gains the upper hand and successfully fights the infectious agent.

Pathological susceptibility to infections

But there are also people who react more sensitively to infectious agents and are therefore sick very often or almost constantly. In addition, infectious diseases can be different and often more severe for them. Experts refer to this as a pathological (pathological) susceptibility to infection.

This is usually due to an immune deficiency. This means that the body’s immune response to a pathogen or to the body’s own degenerated cells is inadequate. However, some immune defects can also cause excessive immune reactions against substances that are foreign or the body’s own.

Experts differentiate between congenital and acquired immune defects:

  • Congenital (primary) immune deficiency: This is when genes change pathologically and ultimately disrupt the body’s defense functions. The defect is inherited and is also referred to as “Inborn Errors of Immunity” (IEI). However, congenital immune defects sometimes only become noticeable in adulthood.
  • Acquired (secondary) immune deficiency : Such an immune deficiency arises as a result of other diseases or external influences. It usually only develops over the course of life.

Congenital immune defects

Primary immunodeficiencies are rare. Depending on the type of congenital immune deficiency, different parts of the immune system are affected.

For example, the development or maturation of both T cells and antibody-producing B cells may be disrupted. This is the case, for example, with Severe Combined Immunodeficiency (SCID) – a life-threatening form of primary immune deficiency.

In variable immunodeficiency syndrome (Common Variable Immunodeficiency, CVID), however, several antibody classes are missing. In selective IgA deficiency, only one class of antibodies ( immunoglobulin A ) is missing.

Warning signs and diagnosis

It is not so easy to distinguish between a pathological and a normal susceptibility to infection. It is not possible to say in general terms how many infections, what type of infections and what course of diseases can be considered normal. How often a person is sick is influenced, among other things, by their living conditions, such as the size of the family or attendance at a daycare center.

The range of symptoms for congenital immune defects is also wide – the type and severity of the symptoms can vary from person to person.

Scientists have therefore defined other parameters for pathological susceptibility to infections because of a primary immune deficiency. These include infections that:

  • last unusually long,
  • bloom again and again,
  • particularly difficult,
  • occur in different or atypical places
  • and/or caused by germs that people with a healthy immune system are unlikely to become ill with.

Disturbed immune regulation – evident in autoimmune reactions such as those in celiac disease – is also a warning sign of a primary immune defect.

With such alarm signals, doctors can use various tests to find out whether there is actually a congenital immune deficiency and what type it is. Various blood tests and immunological examinations, and if necessary, also genetic tests, help.

You can read more about the warning signs of congenital immune defects and the various diagnostic steps in the “Diagnosis” section of our article on immune deficiency.

All newborns are examined for SCID (newborn screening). There is no large-scale early detection program for all other primary immunodeficiencies.


First, doctors try to treat existing infections, for example with antivirals (against viruses), antimycotics (against fungi) or antibiotics (against bacteria). These can also be prescribed as a preventative measure to people with weakened immune systems.

Vaccinations also have a preventive effect against infections. They are therefore particularly advisable for patients with weakened immune systems. You can find out which vaccines are recommended when and what should be taken into account when vaccinating in the event of a weakened immune system in the article Immunosuppression and vaccination.

Further treatment measures for primary immunodeficiencies depend on their type and severity. For example, missing antibodies can be replaced with regular antibody infusions.

If immune regulation is impaired, medications are often used that suppress immune reactions (immunosuppressants such as cortisone). Drugs that kill dysregulated immune cells (such as the artificially produced monoclonal antibody rituximab) can also be helpful.

In some cases it is possible to cure a primary immune deficiency with the help of a stem cell transplant . Researchers are also working on gene therapies against congenital immune defects. A first drug is available in some countries for those affected by SCID.

Acquired immunodeficiencies

A weakness of the immune system does not have to be congenital but can also develop because of external influences. The cause of the most common acquired immune deficiency disease, AIDS (Acquired Immunodeficiency Syndrome), is infection with human immunodeficiency viruses (HIV).

These weaken the immune system of those infected so much that the body can no longer protect itself from harmless pathogens. Cancer cells in particular then have an easier time of it – so the risk of cancer for those affected is increased.

In addition to HIV, many other (chronic) diseases can also impair the immune system, for example:

  • Diabetes mellitus
  • Multiple sclerosis (MS)
  • Cirrhosis of the liver
  • Diseases with impaired kidney function
  • Leukaemia (“blood cancer”)
  • Lymphomas

Even after the spleen has been removed (splenectomy), there is an increased susceptibility to infections, at least for certain infectious pathogens.

In addition, certain therapies also impair the immune system. This applies, for example, to immunosuppressive therapies, such as those necessary for autoimmune diseases and after organ transplants. The body’s immune system is also weakened in people with cancer who receive chemotherapy and/or radiation therapy .

Other causes of susceptibility to infection

In addition to immune defects, various diseases and therapies, other factors influence the immune system. The following lifestyle factors, for example, have a negative effect:

  • persistent stress
  • Consumption of alcohol and nicotine
  • Malnutrition (as in anorexia) or one-sided nutrition
  • Overweight
  • lack of sleep
  • psychological stress
  • physical overload, but also lack of exercise

These factors can weaken the immune system and increase susceptibility to infections. Those affected literally pick up any infection and complain, for example, that they constantly have a cold. However, unlike a pathological immune deficiency, all of these factors can be prevented with a healthy lifestyle.

In addition, as we age, the ability of the immune system to protect the body from pathogens decreases (immunosenescence). Among other things, fewer functional immune cells circulate in the blood. Older people are therefore more susceptible to infections and often develop more severe symptoms of the disease than younger sufferers. This also increases the risk of autoimmune diseases in which the body fights against its own components (for example rheumatoid arthritis).

Pregnant women are also more susceptible to infections. During pregnancy, the immune system adapts to the new situation so that the fetus is not incorrectly identified as a foreign body and rejected. It is therefore particularly important for pregnant women to maintain a healthy lifestyle.

An outlook at UAE’s Residents

UAE has a robust healthcare system and has a pro-active response in the interest of public health. Chronic conditions like diabetes, cardiovascular diseases and obesity which are present in the insured population, can increase their chances to infections resulting in several mild and severe outcomes. With the diverse population and substantial expatriate community, the dynamics of spread and susceptibility varies due to different levels of immunity and exposure as through the member’s home countries. The DHA has taken measures to instruct insurance companies to cover adequately however at their discretion and with adequate declaration forms and medical necessity.