Pathologische Infektionsanfälligkeit

Pathological susceptibility to infection is usually the leading symptom of a primary immunodeficiency. The distinction from physiological susceptibility to infection is difficult, since no current epidemiological data are available on the number, type and course of infectious diseases that can be described as normal at what age (Monto AS et al. 1993). The influence of factors such as social structures, family size or attendance at a day-care centre on the frequency of infection makes it even more difficult to specify an upper limit for the physiological frequency of infection.

Unusual pathogens: Signs of pathological susceptibility to infection may include infections caused by unusual pathogens that rarely lead to severe disease in immunocompetent individuals, such as pneumonia caused by Pneumocystis jirovecii or CMV, Candida sepsis, intestinal and/or biliary tract infection caused by cryptosporidia or microsporidia, or disseminated infection caused by non-tuberculous mycobacteria (NTM) (Bustamante J et al. 2008).

Unusually severe infections with "common" pathogens: Furthermore, unusual, severe infections with "common" pathogens such as pneumococci or herpes simplex viruses may indicate a primary immunodeficiency (Bustamante J et al 2008). The isolated pathogens may already provide a first indication of the underlying immunodeficiency.

Unusual localizations: The localization of the infection can also be an indication of pathological susceptibility to infection. Monotopic infections, for example, are more likely to indicate local anatomical causes, whereas polytopic infections are more likely to indicate a systemic immune deficiency. Pathological susceptibility to infection may also be characterized by atypical localizations of infections, e.g., a brain abscess caused by Aspergillus spp. or a liver abscess caused by S. aureus (Patiroglu T et al. 2010).

Unusual resistance to therapy: The protracted course of infections or an inadequate response to antibiotic therapy are also common indications of pathological susceptibility to infection (Cunningham-Rundles C et al. 1999). For example, a systematic review of the literature on persistent chronic rhinosinusitis reported that up to 50% of patients who did not respond to adequate therapy ultimately had a primary immunodeficiency. Unusual courses after pathogen exposure also include infectious complications due to attenuated pathogens that may occur after live vaccinations, such as BCG vaccination, MMR, varicella, or rotavirus vaccination (Cunningham-Rundles C et al. 1999; Marciano BE et al. 2014).

Finally, the severity (intensity) of infectious diseases may be an expression of pathological susceptibility to infection. Here, the term "major infections" is used to distinguish pneumonia, meningitis, sepsis, osteomyelitis and invasive abscesses from so-called "minor infections", such as otitis media, sinusitis, bronchitis and superficial skin abscesses. Although the occurrence of major infections predominates in primary immunodeficiencies, persistent or recurrent minor infections above the level can also be an expression of a primary immunodeficiency (Aghamohammadi A et al. 2008; Owayed A et al. 2016). The number of infections (the sum) is often perceived as a leading symptom, especially by the affected person or patient's relatives. Infections should be distinguished here from episodes of fever without focus or infection-like symptoms (e.g. obstructive bronchitis).

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