H. INFLUENZAE B DISEASE

Haemophilus influenzae b (Hib) infections are commonest cause of meningitis and pneumonia in young children (6 months-3 years) of developing countries, though the incidence seems to be substantially reduced due to widespread immunization.

Epidemiology: H. influenzae, a gram-negative coccobacilli, exists in capsulated or uncapsulated forms, with 6 serotypes (a-f). Invasive disease is caused by capsulated serotype b, while other serotypes or uncapsulated organisms may cause localized airway disease or invasive disease in immunocompromised host.

High-risk factors: There is a striking age distribution of invasive Hib disease, with gt;90% cases seen within first 5 years of life. In older children, it is more likely in immunocompromised children specially with splenic dysfunction, e.g. sickle cell disease, asplenia and splenectomy.

Pathogenesis: Hib organisms colonize respiratory flora via droplet infections-colonization rate being directly related to age. As colonized individuals develop natural immunity in due course of time, uncolonized infants and young infants are more susceptible for Hib disease at the time of first infection. Infection may spread locally or via hematogenous route to distant sites (invasive disease). Clinical spectrum of Hib disease varies from localized disease, e.g. otitis or sinusitis to invasive disease, i.e. meningitis, pneumonia or septicemia (Table 10.15).

Diagnosis depends on the culture and serotyping of organism, which requires prompt transport and inoculation as the organism is very fastidious.

A latex agglutination test to detect antibodies against capsular polysaccharide antigen, i.e. polysaccharide reactive proteins (PRP) in CSF or other secretions is very useful for early diagnosis, especially in partially-treated cases.

Treatment depends on the severity of disease. While PO Amoxycillin or Co-amoxclav for 7-10 days is usually adequate for localized disease, intensive parenteral therapy with a third-generation cephalosporin, i.e. Ceftriaxone is essential in invasive disease.

Prevention of Hib disease involves:

• Routine Hib immunization with a conjugated polysaccharide vaccine, given at 6,10 and 14 weeks as a combination pentavalent vaccine in NIS, without any booster dose. However, IAP recommends three primary doses as in NIS, along with a booster dose at 12-18 months. Catch-immunization is not recommended beyond 5 years of age, except in high- risk cases. (Ch 9.2.1)

• Post-exposure chemoprophylaxis with Rifampicin (10-20 mg/kg OD for 4 days) is indicated in close contacts of confirmed cases, who are unimmunized and lt;5 years of age.

TABLE 10.15: Clinical spectrum of Hib disease

Localized disease:

• Otitis media

• Sinusitis

• Acute epiglottis

• Others: Orbital cellulitis, conjunctivitis

Invasive disease:

• Meningitis

• Pneumonia

• Bacteremia

• Others: Arthritis, pericarditis, peritonitis