Epidemiology of Haemophilus Influenzae Invasive Disease in Children

ABSTRACT & COMMENTARY

Source: CDC. Haemophilus influenzae invasive disease among children aged younger than 5 years—California, 1990-1996. MMWR Morb Mortal Wkly Rep 1998;47:737-740.

Haemophilus influenzae type b (hib) conjugate vaccines were introduced in 1988 for use in children aged 18 months to 5 years, and in 1990 they were recommended for use beginning at 2 months of age. As a result, the incidence of invasive Hib disease in children younger than 5 years during 1989-1995 has declined by 95%.1 The decline of Hib invasive disease has raised concerns about an increase of Haemophilus influenzae (Hi) invasive disease caused by other serotypes (a, c, d, e, f, and nontypeable). This Centers for Disease Control and Prevention (CDC) report analyzed reported cases of Hib and nontype b Hi invasive disease in children younger than 5 years in California from 1990-1996.

Cases were collected from clinics, laboratories, and hospitals in California, a state where Hi invasive disease has been a reportable disease since 1989. During the 1990-1995 study period, 1014 cases of invasive Hi disease were reported in children younger than 5 years: 591 (58%) with Hib, 160 (16%) with nontype b Hi, and 263 (26%) with unknown Hi serotype.

In 1990, there were 346 reported cases of invasive Hib disease (14 per 100,000), while in 1996 there were only four reports (0.1 per 100,000)—a decrease of 99%. Likewise, the number of reported Hi cases of unknown Hi serotype decreased by 93% from 1990 to 1996. During the same time period, the incidence of nontype b Hi invasive disease remained constant at 0.9 per 100,000.

Commentary by Leonard Friedland, MD

I recall the day in 1988 when I gave my first dose of Hib conjugate vaccine to a patient in my resident clinic. What was once a common cause of invasive disease in young children has miraculously become a very rare disease. I am pleased to have seen this happen during my career. On the flip side, however, it will now be possible for a newly trained emergency physician to never encounter a case of invasive Hib disease! This report documents that, while the introduction of the highly effective Hib conjugate vaccine offers no protection against invasive Hi disease caused by serotypes other than b (nontypeable and a, c, d, e, f), the incidence of nontype b Hi invasive disease has not increased. Consider nontype b Hi invasive disease in your differential of severe clinical illness in children as the clinical presentation of Hi invasive disease may not vary by serotype.

References

1. Bisgard KM, et al. Haemophilus influenzae invasive disease in the United States, 1994-1995: Near disappearance of a child vaccine preventable disease. Emerg Infect Dis 1998;4:229-237.