Haemophilus influenzae infection
Haemophilus influenzae infection is caused by a small, gram-negative bacterium that primarily affects young children, though it can also impact individuals with specific health vulnerabilities. Initially misidentified as the cause of influenza, H. influenzae can lead to a variety of infections, predominantly respiratory tract infections like pneumonia and bronchitis, as well as more severe conditions such as meningitis and epiglottitis. The bacterium exists in encapsulated (notably type B, or Hib) and non-encapsulated forms, with Hib being responsible for the majority of serious cases.
Transmission occurs through respiratory droplets, making unvaccinated young children particularly susceptible, especially those in contact with individuals who have invasive Hib disease. The introduction of the Hib vaccine has significantly reduced the incidence of these infections, with vaccination recommended for infants starting at two months of age. Diagnosis typically involves culturing samples on specialized growth media, and treatment usually includes antibiotics like cephalosporins, with a focus on managing antibiotic resistance. Understanding and managing H. influenzae infections is crucial for public health, especially in vulnerable populations.
Haemophilus influenzae infection
- ANATOMY OR SYSTEM AFFECTED: Brain, ears, lungs, respiratory system
Definition
Haemophilus influenzae is a small, gram-negative bacterium that causes a variety of infections, primarily in young children. The species designation influenzae reflects the earlier misdiagnosis of this bacterium as the cause of influenza, which is a viral disease.
Causes
Strains of H. influenzae may be either encapsulated or nonencapsulated, and six distinct types of capsules are recognized. Most cases of serious invasive disease are caused by type B encapsulated strains (Hib), but bacteria of any subtype may be present as part of the normal respiratory tract flora in healthy persons. Further, the widespread use of the Hib vaccine has caused the incidence of type B infections to dramatically decrease. Humans are the only natural host of the organism, and disease is spread from person to person by inhalation of respiratory droplets or by direct contact with respiratory secretions.
Risk Factors
Young children who are not immunized are at high risk for contracting H. influenzae infections, particularly if contact has been established with a child with invasive Hib disease. Others at risk include people with human immunodeficiency virus (HIV) infection, sickle cell disease, asplenia (absent or nonfunctioning spleen), or malignant neoplasms.
Symptoms
H. influenzae infections can result in a range of symptoms. Most are respiratory tract infections, such as pneumonia, bronchitis, sinusitis, and otitis media, cause symptoms associated with those diseases, such as coughing, sneezing, and pain. Some strains cause invasive diseases and accompanying symptoms, such as meningitis, epiglottitis, bacteremia, cellulitis, and septic arthritis.
Screening and Diagnosis
Persons with a suspected H. influenzae infection may have a sample taken for analysis. In the laboratory, H. influenzae cells are most easily cultured on chocolate agar, a rich growth medium containing essential growth factors from hemolyzed red blood cells. Colonies appear gray, with a diameter of 0.5 to 0.8 millimeters and usually with rough edges. Strains surrounded by a polysaccharide capsule usually produce larger colonies that are somewhat mucoid in appearance.
Prevention and Outcomes
Until 1988, when the effective Hib conjugate vaccines were first introduced, Hib was the most common cause of bacterial meningitis in children in the United States. Acute epiglottitis caused by massive Hib colonization had a high mortality in children aged two to four years. In the years since the widespread use of these vaccines, the incidence of invasive Hib disease in infants and young children has decreased by almost 99 percent.
Two different Hib conjugate vaccines are commercially available in the United States, PRP-T and PRP-OMP, and both show excellent effectiveness with minimal adverse reactions. Children as young as two months of age can be immunized. A two- or three-dose regimen is administered, depending on the vaccine prescribed, and a booster is recommended at age twelve to fifteen months.
Treatment and Therapy
Invasive Hib infections are most commonly treated with a third-generation cephalosporin antibiotic, such as cefotaxime or ceftriaxone. Meropenem, or the combination of chloramphenicol and ampicillin, has also been used effectively. Oral amoxicillin is usually prescribed for localized respiratory tract infections such as otitis media. Because as many as 5 to 50 percent of isolates worldwide are resistant to ampicillin, an oral cephalosporin may also be required. Rifampin has proved successful as a chemoprophylaxis agent in households with at least one contact younger than four years of age because it eliminates Hib from the pharynx in most carriers.
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