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Pneumonia caused by Haemophilus influenzae: causes, symptoms, diagnosis, treatment

Alexey Kryvenko, medical expert
Last reviewed: 06.07.2025

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Haemophilus influenzae (Afanasyev-Pfeiffer hemophilus) is a common causative agent of community-acquired pneumonia. Hemophilus influenzae often lives on the mucous membrane of the upper respiratory tract, can penetrate into the lower respiratory tract and cause exacerbation of chronic bronchitis. Virulent strains have a capsule; according to the antigenic structure, 6 serotypes of H.influenzae are distinguished: a, b, c, d, e, f. Strains containing the b antigen (Hib) are the most virulent and most often cause severe pneumonia, as well as severe damage to the nervous system - meningoencephalitis. The capsular antigen that determines the specificity of H.influenza type b is polyribophosphate.

There are risk groups for pneumonia caused by Haemophilus influenzae:

representatives of low socio-economic strata, who live in poor sanitary, hygienic and economic conditions;
representatives of the black race;
patients with removed spleen;
patients with lymphoproliferative diseases, primarily lymphogranulomatosis;
patients with impaired antibody-forming function;
children under 6 years of age attending nurseries and kindergartens.

Clinical features of pneumonia caused by Haemophilus influenzae

Most often, pneumonia caused by Haemophilus influenzae develops in one-year-old children and is quite severe, with half of the patients developing exudative pleurisy early.

In adult patients, Haemophilus influenzae causes mainly focal pneumonia, which is manifested by fever, cough with the separation of mucopurulent sputum, dullness of percussion sound over the lesion, crepitus and fine bubbling rales. However, pneumonia can be complicated by pleurisy (fibrinous or exudative), pericarditis, arthritis, meningitis and even sepsis.

Diagnostic criteria for pneumonia caused by Haemophilus influenzae

Haemophilus influenzae pneumonia is diagnosed based on the following:

analysis of the corresponding clinical picture described above;
detection of numerous small gram-negative rods in sputum smears stained by Gram;
positive results of sputum and pleural fluid culture on special media - blood or chocolate agar (rabbit or horse blood is added to the agar). In the presence of 5% CO, at a temperature of 37°C, colonies of Haemophilus influenzae grow in 24 hours;
detection of the capsular antigen of Haemophilus influenzae (polyribophosphate) in the patient's blood and urine. For this purpose, latex and coagglutination methods, immunoelectrophoresis, the indirect hemagglutination inhibition reaction, as well as test systems with monoclonal antibodies to the capsular antigen are used.

Treatment of pneumonia caused by Haemophilus influenzae

The first-line antibiotic is ampicillin (amoxicillin) up to 2-4 g per day. In case of resistant strains, a combination of amoxicillin and clavulanate (augmentin) is used. Second- and third-generation cephalosporins, aztreonam, and quinolones are also effective.

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