Infectious diseasesepidemiology and surveillance

Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance and occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility and resistance | Control measures | Outbreak measures

Victorian statutory requirement

Suspected and confirmed Haemophilus influenzae type B (Hib) infections (Group A disease) must be notified immediately by telephone followed by written notification within five days.

Infectious agent

Haemophilus influenzae is a gram-negative coccobacillus. Invasive infections are commonly caused by serotype B.

Identification

Clinical features
Meningitis
The onset can be sub-acute or sudden with fever, vomiting, lethargy and meningeal irritation with a bulging fontanelle in infants and stiff neck and back in older children.

Epiglottitis
The patient is usually a child and presents with signs of upper respiratory tract obstruction and a characteristic expiratory snore, difficulty in swallowing with drooling of saliva, irritability, restlessness and fever. Progression of the infection can lead to complete respiratory obstruction.

H. influenzae type b infection may also cause other diseases such as pneumonia, septic arthritis, cellulitis and osteomyelitis.

Method of diagnosis
Clinical diagnosis is confirmed in the laboratory by:

• isolation of Hib from a normally sterile site such as blood or cerebrospinal fluid, typing should be confirmed by an approved reference laboratory
• detection of Hib antigen in CSF when other laboratory parameters are consistent with bacterial meningitis, and when there has been no Hib vaccination within 21 days of onset.
• Body fluids and urine may give positive antigen reactions for Hib for up to 21 days after vaccination.

Incubation period

The incubation period is uncertain. It is probably two to four days.

Public health significance & occurrence

Prior to 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 at least 500 cases of Hib disease annually in Australian in children less than six years of age. There were 10–15 deaths per year and 20–40% of survivors were left with permanent neurological damage.

Indigenous 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 reduced by more than 90%. 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.

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

Humans.

Mode of transmission

Hib is transmitted person to person through respiratory droplet spread and may also be rarely acquired through contact with infected respiratory discharges.

Period of communicability

Hib is communicable for as long as the organisms are present in the nasopharynx. Patients are no longer infectious once they have received 24 to 48 hours of appropriate antibiotic therapy.

Susceptibility & resistance

Sustained immunity is conferred through immunisation or prior infection. Maternal antibody provides passive immunity for a variable time period after birth.

Infection does not always result in immunity. This is particularly evident in children less than two 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, though late secondary cases have been reported.

Control measures

Preventive measures
Routine childhood immunisation remains the most important preventive measure against Hib disease. Hib vaccine is recommended as part of the Australian Standard Vaccination Schedule for all children at two, four and 12 months of age and for older persons with asplenia. Refer to the current edition of the Australian immunisation handbook (National Health and Medical Research Council) for further details.

Before and after splenectomy
Hib is an uncommon cause of post-splenectomy sepsis in adults and children. Children over two years of age who are fully immunised do not require a Hib booster following splenectomy. A single dose is recommended for any other individuals (regardless of age) if incompletely or unvaccinated who have close contact with children less than five years. No booster doses are required.

If possible the vaccine should be given at least two weeks before splenectomy.

Control of case
Intravenous cefotaxime or ceftriaxone may be used for empirical therapy until antibiotic sensitivities are known. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited) and seek expert infectious disease advice.

These antibiotics do not clear Hib from the nasopharynx. Rifampicin should be given to cases prior to discharge from hospital to ensure clearance of the organism. If the treated patient is less than two years of age and has not been immunised, a course of Hib vaccine should still be given after discharge from hospital.

Respiratory isolation procedures are recommended for 24 hours after the start of treatment.

Concurrent or terminal disinfection of possibly contaminated items is not generally required.

Control of contacts
Unvaccinated contacts less than five years of age should be immunised as soon as possible.

Household contacts
Parents of confirmed cases should be educated about the risks of secondary cases in siblings and other close contacts under five years of age, and seek early medical review if any close contacts develop symptoms consistent with Hib disease.

Chemoprophylaxis (see below) is indicated for household contacts only if:

• the household of a case contains one or more infants under seven months of age regardless of vaccination status, or
• the household of a case contains one or more children aged seven months to five years who are not age-appropriately immunised against Hib according to the current Australian Standard Vaccination Schedule.

In either setting, all persons in the same household should receive chemoprophylaxis and inadequately vaccinated children should receive age appropriate Hib vaccination.

Child care
If the case attends a child care facility for more than 18 hours a week and other children less than two years of age in this facility are in close contact, chemoprophylaxis should be given to all contacts including staff if any of the close contacts are inadequately vaccinated.
Chemoprophylaxis does not eliminate the need for surveillance and parents of contacts should be advised of the risk of late secondary cases despite prophylaxis.

Chemoprophylaxis
Decisions about the use and advice about contra-indications, dosing and supply of rifampicin for chemoprophylaxis should always be made in consultation with the Department of Health. For adverse effects and contra-indications to rifampicin, see section on meningococcal disease.

Control of environment
See Outbreak measures, below.

Outbreak measures

Outbreaks of Hib are now rare. The public health response to a cluster of Hib cases is based on the control principles outlined above in Control of contacts, which may require expansion in the extent of contact surveillance, chemoprophylaxis and vaccination.