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A review of the role of Haemophilus influenzae in community-acquired pneumonia

Community-acquired pneumonia (CAP) is a major cause of morbidity and mortality in children and adults. Those at the greatest risk are young children in developing countries, the elderly, and those with chronic respiratory disease. The implementation of pneumococcal and Haemophilus influenzae type b (Hib) conjugate vaccination in many countries has resulted in a reduction in the global number of CAP episodes in young children over the past decade, but pneumonia remains a leading cause of morbidity and mortality in this age group.

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 Clinical Features and Outcomes of Community-Acquired Pneumonia Caused by Haemophilus influenzae

Haemophilus influenzae has become nearly equally as common a cause of pneumonia as Streptococcus pneumoniae. The same patient populations appear to be susceptible, but pneumonia caused by Haemophilus is less severe by many criteria, including the absence of altered mental status, extreme leukocytosis or leukopenia, bacteremia, septic shock, and death.

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Factsheet about Invasive Haemophilus influenzae disease

Haemophilus influenzae type b is responsible for 95% of all invasive H. influenzae infections in unimmunised populations and it is an important cause of severe and sometimes fatal infections, particularly in young children. Routine immunisation has resulted in a remarkable decline in serious Hib disease and has practically eliminated Hib meningitis among vaccinated infants and young children.

Haemophilus influenzae and the lung (Haemophilus and the lung)

This bacterium is divided into typeable forms (such as type b) or nontypeable forms based on the presence or absence of a tough polysaccharide capsule. Respiratory disease is predominantly caused by the nontypeable forms (NTHi). NTHi is also one of the leading causes of pneumonia in adults (with Streptococcus pneumoniaeand Moxarellacatarrhalis). Most patients with NTHi pneumonia have bronchopneumonia with cough, fever and systemic upset. The illness is generally less fulminant than that with S. pneumoniae and commonly occurs in patients with underlying lung disease (particularly COPD).

What is the best treatment?

The favored regimens for treatment of invasive infections caused by type b strains, including meningitis and epiglottitis, are intravenous cefotaxime or ceftriaxone.

Resources

CDC

Haemophilus influenzae, a type of bacteria, can cause many different kinds of infections. These infections range from mild, like ear infections, to serious, like bloodstream infections.

StatPearls

Clinical features depend on the organ infected by H. influenzae, and history and physical examination are geared towards positive and negative findings in the system involved. The most common presentation is pneumonia, which presents as high-grade fever, chills, productive purulent cough, shortness of breath, chest pain, lethargy, and generalized body aches. It is often clinically indistinguishable from other causes of bacterial pneumonia and is a frequent underlying pathogen in CAP patients who had a history of complete pneumococcal vaccination or have already diagnosed respiratory illnesses.