- Haemophilus influenzae type b (Hib) infection is an ‘urgent’ notifiable condition that must be notified immediately to the department by medical practitioners and pathology services.
- Hib infections cause invasive disease such as meningitis, epiglottitis, pneumonia, arthritis and cellulitis.
- Routine childhood immunisation is the most important preventive measure against Hib disease.
- Due to widespread vaccination, Hib outbreaks are now rare in Australia.
Notification requirement for Haemophilus influenzae infections
Haemophilus influenzae type b (Hib) infection is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days.
This is a Victorian statutory requirement.
Primary school and children’s services centre exclusion for Haemophilus influenzae infections
A case of Hib must be excluded from primary school or children’s services centres until at least 4 days of appropriate antibiotic treatment has been completed.
Infectious agent of Haemophilus influenzae infections
Haemophilus influenzae is a Gram-negative coccobacillus that is a normal part of the upper respiratory tract flora. There are nontypable (NT) strains that may cause invasive disease, but these are generally less virulent than the capsular types (a to f). Invasive infections are commonly caused by H. influenzae serotype b (Hib). Non–serotype b infections are not notifiable.
Identification of Haemophilus influenzae infections
Invasive disease can affect many organ systems. The most common types of invasive disease are meningitis, epiglottitis, pneumonia, arthritis and cellulitis.
Meningitis is an infection of the membranes covering the brain. The onset can be subacute or sudden, with fever, vomiting, lethargy, meningeal irritation, a bulging fontanelle in infants, and stiff neck and back in older children. The classical signs of meningitis, such as neck stiffness and photophobia, are often not detected in infants, who may present with drowsiness, poor feeding and high fever.
Epiglottitis is an infection and swelling of the epiglottis, the tissue in the throat that covers and protects the larynx during swallowing. The patient is usually a child, and presents with signs of upper respiratory tract obstruction, and a characteristic soft stridor and drooling. A pale, febrile, anxious child who remains upright to maximise their airway is suggestive of epiglottitis. Progression of the infection can lead to complete respiratory obstruction. Vaccination has made epiglottitis caused by Hib a much rarer illness.
Meningitis and epiglottitis are nearly always fatal without appropriate treatment.
Hib infection may also cause other diseases, such as pneumonia, septic arthritis (joint infection), cellulitis (rapidly progressing skin infection, which usually involves the face, head or neck) and otitis media (infection of the middle ear). Less common infections include purulent pericarditis, endocarditis and osteomyelitis (bone infection).
Clinical diagnosis is confirmed in the laboratory by a positive culture of H. influenzae from a normally sterile site, such as blood, cerebrospinal fluid, pleural fluid or joint fluid.
All isolates should be serotyped by an approved reference laboratory to determine whether the isolate is type b.
Incubation period of Haemophilus influenzae
The incubation period is uncertain. It is probably 2–4 days.
Public health significance and occurrence of Haemophilus influenzae infections
Before the introduction of Hib vaccine to the routine immunisation schedule in 1993, Hib disease was the most common serious invasive bacterial infection in children. At this time, there were at least 500 cases of Hib disease annually in Australia in children under 6 years of age. There were 10–15 deaths per year, and 40 per cent of survivors had neurological sequelae such as deafness and intellectual impairment.
Aboriginal and Torres Strait Islander children were at five to six times greater risk of developing Hib disease and acquired it at a much younger age than non-Indigenous children.
By 1998, the number of notified cases in Australia had decreased by more than 90 per cent. The number of notified cases has continued to fall. Invasive Hib disease is now only very rarely seen in Victorian children. There has been no evidence of a shift in Hib cases to older age groups.
Hib epiglottitis may still occur, particularly in adults and unimmunised children. This diagnosis should still be considered when a person presents with fever and signs of upper respiratory obstruction resembling croup. Other previously rare bacterial causes of epiglottitis may now be more likely diagnoses, particularly streptococci and Staphylococcus aureus.
Immunosuppressed individuals of any age remain at risk from Hib infection. Asplenic patients are at greater risk of infection if they have not been appropriately immunised.
Reservoir of Haemophilus influenzae
Humans are the reservoir, via asymptomatic carriage, most commonly in young children.
Mode of transmission of Haemophilus influenzae
Hib is transmitted from person to person through respiratory droplet spread. It may also be rarely acquired through contact with infected respiratory discharges.
Period of communicability of Haemophilus influenzae infections
Hib is communicable for as long as the organisms are present in the nasopharynx. Certain circumstances, particularly close contact with a case (such as in a household, childcare or institutional setting), can lead to outbreaks or direct secondary cases.
Patients are no longer infectious once they have received 24–48 hours of appropriate antibiotic therapy.
Susceptibility and resistance to Haemophilus influenzae infections
Sustained immunity is conferred through immunisation or prior infection. Maternal antibody provides passive immunity for a variable time after birth.
Infection does not always result in immunity, however. This is particularly evident in children less than 2 years of age, who are unable to mount an antibody response to the type b capsular polysaccharide, even following invasive disease.
Most secondary cases among close contacts occur within the first week after exposure, although late secondary cases have been reported.
Control measures for Haemophilus influenzae infections
Routine childhood immunisation remains the most important preventive measure against Hib disease. Hib vaccine is recommended for all children from 2 months of age and for older people with asplenia. Refer to the Australian immunisation handbook for Hib immunisation recommendations.
Before and after splenectomy
Hib is an uncommon cause of post-splenectomy sepsis in adults and children. Children older than 2 years who have received all scheduled doses of Hib vaccine do not require a booster dose after splenectomy. A single does of Hib vaccine is recommended for other splenectomised individuals who were not vaccinated in infancy or are incompletely vaccinated.
If possible, the vaccine should be given at least 2 weeks before splenectomy, or at least 7 days after, to optimise the immune response.
Subsequent booster doses of Hib vaccine are not required.
Control of case
Intravenous ceftriaxone or cefotaxime may be used for empirical therapy until antibiotic sensitivities are known. Consult the current version of Therapeutic guidelines: antibiotic and seek expert infectious disease advice.
Not all antibiotics clear Hib from the nasopharynx. Contact the department and seek expert infectious disease advice if considering the need for clearance antibiotics.
Unimmunised and partially immunised cases less than 2 years of age should complete their primary vaccination course. Fully vaccinated cases need assessment as they may require testing of Hib antibody levels and investigation for an immune deficiency.
Respiratory isolation procedures are recommended for 24 hours after the start of treatment.
Control of contacts
Unvaccinated contacts less than 5 years of age should be immunised as soon as possible.
Parents of confirmed cases should be educated about the risks of secondary cases in siblings and other close contacts under 5 years of age. They should seek early medical review if any close contacts develop symptoms consistent with Hib disease.
Chemoprophylaxis (see below) is indicated for household contacts. These are defined as people living in the same house as the case (or recent visitors who stayed overnight in the 7 days preceding the onset of the case’s illness), if the household contains a vulnerable individual.
Vulnerable individuals are defined as:
- one or more infants under 7 months of age, regardless of vaccination status
- one or more children aged 7 months to 5 years who are not age-appropriately immunised against Hib according to the current National Immunisation Program schedule
- one or more immunosuppressed or asplenic individuals of any age.
In these settings, all people in the same household should receive chemoprophylaxis, and inadequately vaccinated children should receive age-appropriate Hib vaccination.
Chemoprophylaxis should be given to all children and staff of a childcare or family day-care centre who were in the same room group as the case in the 7 days preceding the onset of illness, if the case attends childcare for more than 18 hours a week and the centre contains a vulnerable individual (as above).
Chemoprophylaxis does not eliminate the need for surveillance, and parents of contacts should be advised of the risk of late secondary cases despite prophylaxis.
Decisions about the use of chemoprophylaxis, and advice about contraindications, dosing and supply of chemoprophylaxis, should always be made in consultation with the department.
Control of environment
See ‘Outbreak measures’.
Outbreak measures for Haemophilus influenzae infections
Outbreaks of Hib are now rare. The public health response to a cluster of Hib cases is based on the control principles outlined above under ‘Control of contacts’, which – in the event of an outbreak – may require expansion in the extent of contact surveillance, chemoprophylaxis and vaccination.
Reviewed 08 October 2015