1. What are frequent infections?
We speak of frequent infections when someone falls ill markedly more often than average — repeatedly with respiratory infections (a cold, bronchitis, sinusitis), urinary tract infections, skin infections or a combination.
The frequency alone, however, says nothing yet about the immune system. What is decisive is how severe the infections are, how fast they follow one another and whether unusual pathogens are involved. A healthy immune system needs regular contact with pathogens — especially in children, an increased infection rate is a normal part of immune maturation.
The distinction is important: frequent, mild infections usually point to increased strain (stress, lack of sleep, poor nutrition) or exposure (children, caring professions). Severe, atypical or recurrent bacterial infections, on the other hand, can be indications of a true immunodeficiency.
2. What is normal — and what isn't?
Normal frequency
- Adults: 2–4 colds per year — mostly in autumn and winter
- Children of nursery age: 8–12 respiratory infections per year — immune maturation takes several years
- School-age children: 4–8 infections per year — usually much milder than in toddlers
- Older people: often longer recovery times, but not necessarily more infections
Signs of a relevant immunodeficiency
The ELVIS criteria of the German Society for Immunology help with the classification. Notable are (the acronym follows the German initials):
- Erreger (pathogens): unusual or opportunistic pathogens (e.g. Pneumocystis jirovecii, atypical mycobacteria)
- Lokalisation (localization): infections at atypical sites (brain abscess, bone marrow)
- Verlauf (course): unusually severe, protracted or recurrent
- Intensität (intensity): severe courses despite adequate therapy
- Summe (sum): more than 8 respiratory infections/year in adults, more than 2 severe sinusitis/pneumonia episodes/year, recurrent skin abscesses, recurrent invasive infections
Even with just one point of the ELVIS criteria, the possibility of an immunodeficiency or an underlying condition should be assessed by a doctor.
3. Common causes in adults
Stress and lack of sleep
Chronic stress raises cortisol — which dampens the immune response. Sleep disorders and a sleep deficit (less than 6 hours) have been shown to double the risk of infection with cold viruses.
Iron, vitamin D and zinc deficiency
Iron deficiency anaemia weakens the cellular immune response. Vitamin D deficiency is very common in Germany, especially in winter, and is associated with an increased susceptibility to infection. Zinc deficiency impairs T-cell function. These deficiencies are measurable in the blood and readily treatable.
Diabetes mellitus
Diabetes — especially when poorly controlled — markedly weakens the immune system. Typical consequences: more frequent urinary tract infections, more poorly healing wounds, skin infections, increased respiratory infections.
Chronic diseases
COPD, asthma, chronic kidney diseases, liver cirrhosis, HIV infection, cancers and inflammatory bowel diseases such as Crohn's disease often go hand in hand with an increased susceptibility to infection.
Smoking and alcohol
Smoking damages the ciliated epithelium of the airways and makes you more susceptible to bronchitis and pneumonia. Chronic alcohol consumption suppresses immune function and markedly increases the risk of pneumonia.
Primary immunodeficiencies (PID)
Congenital defects of the immune system are rare but important — the most common form is selective IgA deficiency (about 1:500) and common variable immunodeficiency (CVID). First manifestation is often in adulthood, underdiagnosed for many years. Indications: recurrent bacterial respiratory infections, chronic diarrhoea, autoimmune phenomena.
4. Frequent infections in children
In children, an increased infection rate in the first years of life is physiological — the immune system matures only through repeated contact with pathogens. Especially in the first nursery year, 8–12 respiratory infections per year are normal.
Notable in children:
- recurrent purulent middle ear infections (more than 8/year)
- repeated pneumonia or bronchitis requiring antibiotics
- unusual pathogens (Pneumocystis, atypical mycobacteria)
- failure to thrive, persistent diarrhoea, oral thrush beyond infancy
- a family history of immunodeficiencies
With these indications, a paediatric or immunological assessment should take place. Early diagnosis of primary immunodeficiencies considerably improves the prognosis.
5. When to see a doctor? (warning signs)
Have it assessed by a doctor promptly if:
- infections occur markedly more often than in comparable people
- antibiotics repeatedly show no decisive effect
- infections run an unusually severe or long course
- recurrent pneumonia, severe sinusitis or skin abscesses occur
- there is accompanying unintentional weight loss, night sweats, tiredness or swollen lymph nodes
- there are indications of immunodeficiencies in the family
- new medications (corticosteroids, immunosuppressants, biologics) are being taken
Seek medical help immediately with high fever and a reduced general condition, shortness of breath, altered consciousness, severe shivering or indications of sepsis (cold sweat, confusion, very rapid breathing).
