Is Hib Contagious?
H. influenzae type b (Hib), along with all H. influenzae types, including both non-b and nontypeable H. influenzae, are contagious. H. influenzae is spread by direct contact with the respiratory secretions of someone who is a carrier or is infected with H. influenzae. Less commonly, infection can be spread to newborn infants if they come into contact with genital or amniotic fluid from an infected mother during the birth process.1
H. influenzae enters the body through the upper respiratory tract, and can remain there for several months without causing illness. 2 Nontypeable strains of H. influenzae colonize in the respiratory tract of approximately 75 percent of healthy adults. Currently, Hib is believed to colonize in the back of the throat in 3 to 5 percent of children.3 In some individuals, the organism causes an invasive infection such as pneumonia or meningitis. Although it is not known how H. influenzae enters the bloodstream, it is possible that a co-existing viral or mycoplasma infection of the upper respiratory tract may be a contributing factor.4
In general, H. influenzae disease is considered to be minimally contagious, however, if a person has close contact to someone who is infected with or is carrying H. influenzae, transmission can occur.5 Hib has the potential to spread quickly in populations in enclosed quarters, such as families, institutional settings, and daycare centers.6 Prior to the introduction of Hib vaccines in the United States, health officials had identified a seasonal pattern to Hib, with the first peak between the months of September and December, and the second peak between March and May.7
In the United States, before Hib vaccines became available, approximately two-thirds of all cases of Hib invasive disease affected infants and children under 15 months of age 8 and 85 percent of cases occurred in children under the age of 5.9 Following the introduction of the Hib vaccine, the burden of invasive H. influenzae disease has shifted from children to adults, and most particularly seniors over the age of 65.10 11 A 2011 published study found that between 1998 and 2008, 51 percent of invasive H. influenzae cases involved adults over the age of 65. Death rates from H. influenzae disease were also found to be significantly higher among seniors over age 65, with 67 percent of infections resulting in death.12
IMPORTANT NOTE: NVIC encourages you to become fully informed about Haemophilus Influenzae Type B (Hib) and the Hib vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.
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1 CDC Haemophilus influenzae Disease (including Hib) – For Clinicians. Feb. 13, 2018
2 CDC Haemophilus influenzae type b – Pathogenesis Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.
3 Rathore MH Pediatric Haemophilus Influenzae Infection - Epidemiology Medscape Apr. 4, 2016
4 CDC Haemophilus influenzae type b – Pathogenesis Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.
7 CDC Haemophilus influenzae type b - Epidemiology Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.
8 Broome CV. Epidemiology of Haemophilus influenzae type b Infections in the United States. Pediatr Infect Dis J. 1987 Aug; 6(8):779-82.
9 Rathore MH Pediatric Haemophilus Influenzae Infection - Epidemiology Medscape Apr. 4, 2016
10 Mann D. Hib Disease Increasing Among Adults. WebMD. Aug. 11, 2011
11 Blain A, MacNeil J, Wang X, et al. Invasive Haemophilus influenzae Disease in Adults ≥65 Years, United States, 2011 Open Forum Infect Dis. 2014 Sep; 1(2): ofu044.
12 Rubach MP, Bender JM, Mottice S et al. Increasing Incidence of Invasive Haemophilus influenzae Disease in Adults, Utah, USA Emerg Infect Dis. 2011 Sep; 17(9): 1645–1650.