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    Infectious Disease Prevention Section
    Mail Code: 1927
    PO BOX 149347 - Austin, TX 78714-9347
    1100 West 49th Street, Suite G401
    Austin, TX 78714

    Phone: (512) 776-7676
    Fax: (512) 776-7616


Haemophilus influenzae

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Organism, Causative Agent, or Etiologic Agent
Invasive Haemophilus influenzae disease can be caused by six identifiable types of H. influenzae bacteria (types a through f) or non-typeable H. influenzae bacteria. Haemophilus influenzae, type b (Hib) usually causes the most severe disease and is the only type that is vaccine preventable. However, all cases of invasive Haemophilus influenzae disease are reportable in Texas. 

Direct contact with respiratory droplets from a carrier or case patient.

Although all types of Haemophilus influenzae can cause illness, Hib is most often the cause of severe disease. The most common and severe manifestation of invasive Haemophilus influenzae disease is meningitis (inflammation and swelling in the coverings of the brain and spinal cord). Symptoms of meningitis include fever, weakness, vomiting, and a stiff neck. Hib and other types of H. influenzae can also cause infection of the lungs, blood, joints, bones, throat, and covering of the heart. Symptoms depend on the part of the body affected.

Incubation Period
The incubation period is hard to define, because most persons who acquire Haemophilus influenzae infections are asymptomatically colonized. Those who become ill following exposure to a case usually do so within 10 days, although the risk may be slightly elevated for up to 60 days. 

As long as the organism is present in discharges from the nose or throat, a person can be contagious to others during the infectious period. Communicability ends within 24 hours of initiation of appropriate chemoprophylaxis. Note, however, that treatment of invasive disease does not necessarily eradicate the organism from the nose/throat. Those exposed more than 7 days before onset of illness in the case are not at significantly increased risk. Hib cases are probably most infectious during the 3 days prior to onset of symptoms.

Invasive Hib disease can be prevented by giving the Hib vaccine to kids 2-18 months of age. Also, Hib and other types of H. influenzae can be prevented by maintaining respiratory isolation for patients and applying good hand-washing technique.

School Exclusion Policy
Children with bacterial meningitis, like that caused by Haemophilus influenzae, should be kept out of school or childcare until they have written permission from a healthcare provider and until they are fever free for 24 hours without the use of fever suppressing medications. Rules for exclusion of sick children from school and childcare are outlined in the Texas Administrative Code, specifically 25 Tex. Admin. Code §97.7.

Recent Texas Trends
Haemophilus influenzae (all serotypes) have been steadily increasing between 2016 to 2018 from 317 to 464 cases respectively. In 2019, cases dropped to 452 and 2020 cases dropped to 206. Prior to 2016, only invasive disease caused by H. influenzae type b (Hib) was reportable. Hib disease is rare in Texas. Since 2000, there have been an average of 9 (range of 2-15) Hib cases reported each year in Texas with 5 reported in 2018 and 9 in 2019. The majority of Haemophilus influenzae cases reported were the non-typeable strain also seen at the national level.  Most cases of Haemophilus influenzae occur in older adults with other underlying conditions that make them susceptible to Haemophilus influenzae.
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Last updated July 25, 2022