Description

Infection with the bacterium Haemophilus influenzae type b (Hib) can result in meningitis and other severe infections (e.g., pneumonia, bacteremia, cellulitis, septic arthritis, and epiglottitis) primarily among infants and children <5 years of age (1). Hib disease is uncommon in anyone 5 years of age or older. Hib meningitis has a case-fatality ratio of 5-10% in the United States even with initiation of early antimicrobial therapy (1). As a result of the widespread use of conjugate Hib vaccines, the disease is now uncommon in the United States and is seen primarily in infants too young to be vaccinated and unvaccinated children. In 2004, the estimated annual incidence of Hib was 0.15 cases per 100,000 in children younger than 5 years of age (2).

Occurrence

Invasive Hib disease is endemic throughout the world. In countries that have achieved high coverage with routine Hib vaccination programs, Hib disease has become rare. In 2004, most countries in Western Europe, South America, and Central America had initiated routine Hib vaccination (http://www.who.int/mediacentre/factsheets/fs294/en/). However, Hib disease remains common in many developing countries and is estimated to cause 2-3 million cases of serious disease in young children annually (3).

Risk for Travelers

Unvaccinated infants and children aged less than 5 years who travel may be at risk for serious Hib disease, especially if traveling to a country that does not use Hib vaccine. In addition, adults who have been splenectomized have an increased risk of infections.

Clinical Presentation

The presentation of Hib disease in children depends on the localization of the infection, which usually occurs when the bacteria enters the bloodstream via the mucosa of the nasopharynx. Meningitis, pneumonia, sepsis, cellulitis, or arthritis caused by Hib resembles these conditions caused by other bacteria. Epiglottitis, a presentation of Hib disease in infants and incompletely vaccinated children younger than 5 years of age, presents as sudden onset of fever, drooling, and difficulty swallowing, and can rapidly progress to airway obstruction.

Prevention

VACCINE

Three conjugate Hib vaccines are licensed for use in infants and children in the United States: HbOC (HibTiTER, Wyeth-Lederle), PRP-OMP (PedvaxHIB, Merck & Co., Inc.), and PRP-T (ActHIB, Sanofi Pasteur; OmniHIB, GlaxoSmithKline). PRP-OMP vaccine is available as a combined product with hepatitis B vaccine (Comvax). PRP-T (ActHIB) and acellular pertussis vaccine (DTaP, Tripedia) are available in the same package and can be combined by the provider; the combined product is called TriHIBit. TriHIBit is licensed for use only as the fourth dose of the Hib and DTaP series; it should not be given for the first, second, or third doses of the Hib series (4).

All infants should receive a primary series of conjugate Hib vaccine beginning at age 2 months (Table 8-2).The number of doses in the primary series depends on the type of vaccine used and the age that vaccination is started. If started at 2 months of age, a primary series of PRP-OMP vaccine consists of two doses; HbOC and PRP-T require a three-dose primary series (Table 4-2). A booster should be given at age 12-15 months, regardless of which vaccine is used for the primary series (5).

The optimal interval between doses is 2 months, with a minimum interval of 1 month. At least 2 months should separate the booster dose from the previous (second or third) dose. Hib vaccines may be given simultaneously at separate sites with all other vaccines.

Limited data suggest that Hib conjugate vaccines given to infants younger than 6 weeks of age may result in a reduced antibody response. Therefore, Hib vaccines, including combination vaccines that contain Hib conjugate, should not be given to infants younger than 6 weeks of age (1).

Any of the conjugate Hib vaccines licensed for use in infants can be substituted in the primary series. If it is necessary to change the type of vaccine, three doses of any combination constitute the primary series. Any licensed conjugate vaccine may be used for the booster dose, regardless of what type was received in the primary series.

Unvaccinated infants and children ages 7 months and older might not require a full series of three or four doses (Table 8-4: catch-up vaccination schedule). The number of doses an infant or a child needs to complete the series depends on the infant’s or child’s age and, to a lesser degree, on the number of prior doses of Hib vaccine received. Previously unvaccinated children 15-59 months of age should receive a single dose of any conjugate Hib vaccine. In general, children older than 59 months of age do not need Hib vaccination. Refer to the American Academy of Pediatrics Red Book (http://aapredbook.aappublications.org) for additional information on late or lapsed Hib vaccination schedules.

Splenectomized persons who have not already been appropriately immunized should receive one dose of Hib vaccine.

Adverse Reactions

Adverse events following vaccination with Hib conjugates are uncommon. Swelling, redness, or pain, or a combination of these, have been reported in 5%-35% of recipients and usually resolve within 12-24 hours (4). Systemic reactions such as fever and irritability are infrequent.

Precautions and Contraindications

Vaccination with Hib conjugate vaccine is contraindicated in anyone known to have experienced anaphylaxis following a prior dose of that vaccine. Vaccination should be delayed in infants and children with moderate or severe acute illnesses. Minor illnesses (for example, mild upper respiratory infection) are not contraindications to vaccination. Contraindications and precautions for the use of TriHIBit and Comvax are the same as those for their individual component vaccines (i.e., DTaP, Hib, and hepatitis B).

Treatment

Specific parenteral antibiotic treatment is necessary for invasive Hib disease, and immediate airway stabilization is necessary for epiglottitis. Antibiotic prophylaxis with rifampin is indicated for all household contacts in the following circumstances: households with a contact aged 4 years or younger who is unimmunized or underimmunized, households with a child aged younger than 12 months who has not received the primary series, and households with an immunocompromised child. Chemoprophylaxis is not recommended for pregnant women or for child care contacts with a single index case, but the children’s vaccination history should be reviewed to ensure completion of the recommended schedule of Hib conjugate vaccine. A 4-day course of rifampin eradicates Hib carriage from the pharynx in approximately 95% of carriers (4).

References

1. Wenger JD, Ward JI. Haemophilus influenzae vaccine. In: Plotkin SA, Orenstein WA, eds. Vaccines. 4th ed. Philadelphia: W.B. Saunders; 2004:229-68.
2. CDC. Active Bacterial Core Surveillance Report, Emerging Infections Program Network, Haemophilus influenzae, 2004 - provisional. Atlanta: Department of Health and Human Services; 2005.
3. Peltola H. Burden of meningitis and other severe bacterial infections of children in Africa: implications for prevention. Clin Infect Dis. 2001;31:64-75.
4. American Academy of Pediatrics. Haemophilus influenzae infections. In: Pickering LK, ed. Red Book: 2006 Report of the Committee on Infectious Diseases. 27th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2006:310-318.
5. CDC. Haemophilus b conjugate vaccines for prevention of Haemophilus influenzae type b disease among infants and children two months of age and older: recommendations of the ACIP. MMWR Recomm Rep. 1991;40(RR-01):1-7.

TABLE 4-02. Recommended Haemophilus influenzae type b (Hib) routine vaccination