Haemophilus influenzae type b

Overview

Haemophilus influenzae type b (Hib) is a gram-negative coccobacillus bacterium that can cause severe illnesses such as pneumonia, bacteraemia and meningitis.

Disease epidemiology

Colonisation by Hib occurred in 3% to 5% of children in the pre-vaccine era, reducing after widespread immunisation to <1%. In developing countries, where routine vaccination with Hib vaccine is not widely available, Hib remains a major cause of invasive diseases. (e.g. meningitis, lower respiratory tract infections and sepsis in infants and children). In Singapore, Hib vaccination was included in the National Childhood Immunisation Programme in May 2013.

Pathogen(s)

Hib, a gram-negative coccobacillus bacterium.

Transmission

Hib primarily transmits through direct deposition of infectious respiratory particles (IRPs) such as when an infected person coughs or sneezes. It can also spread via contact with contaminated surfaces such as when IRPs settle on surfaces or transfer through direct contact (e.g. handshake) before reaching the mouth, nose or eyes. Intrapartum acquisition of infection in neonates may occur by aspiration of amniotic fluid or by contact with maternal genital tract secretions.

Incubation period: Unknown, could range from 2 to 4 days.

Infectious period: Hib is communicable for as long as the organism remains within the nasopharynx (which can be for weeks to months). Cases are no longer infectious once they have received at least 24 hours of the appropriate antibiotics.

Clinical features

Hib disease can result in various clinical syndromes, including pneumonia, occult bacteriemia, meningitis, epiglottitis, septic arthritis, cellulitis, otitis media, purulent pericarditis, and less commonly, endocarditis, endophthalmitis, osteomyelitis, and peritonitis.

Meningitis: symptoms include fever, lethargy, irritability and vomiting (there may be prior symptoms of a respiratory tract infection). There may occasionally be rapid neurological deterioration with respiratory arrest. Shock is present in 20% of cases and may be associated with coagulopathy and purpura. Complications include subdural effusions or empyema, cortical infarction, intracerebral abscess and hydrocephalus. Up to 20% of patients who survive Hib meningitis have permanent hearing loss or other long-term neurological sequelae.

Epiglottitis: Symptoms include high fever, sore throat, stridor and dyspnea with rapid progression to dysphagia, pooling of secretions and drooling. The patient is usually restless and anxious and adopts a sitting position with neck extended and chin protruding to reduce airway obstruction. Rapid deterioration can occur and cause death unless an artificial airway is established.

Pneumonia: There is typically a consolidative pulmonary infiltrate and evidence of pleural involvement in 50% of cases on chest radiograph. Concomitant meningitis or epiglottitis is present in 25% of patients. Purulent pericarditis is a complication resulting from contiguous spread of infection and these patients usually have severe dyspnoea, tachycardia and cardiac failure.

Septic arthritis and osteomyelitis: Prior to conjugate vaccine introduction, Hib was the commonest cause of pyogenic arthritis in children under 2 years of age. Contiguous osteomyelitis in present in 10% to 20% of cases.

Cellulitis: This is usually seen in young children and is the result of a metastatic focus of bacteraemia. Symptoms and signs include fever and an area of warmth, tenderness and erythema (or violaceous discolouration) over the cheek or periorbital area. Bloodstream infection is usually present concomitantly and another focus of infection (e.g. meningitis) develops in about 10% of cases.

Risk factors

All persons who are unvaccinated or partially vaccinated.

Diagnosis

Detection of Hib via isolation, antigen detection or polymerase chain reaction from sterile body fluids e.g. blood, CSF and pleural fluid.

Treatment and management

Antibiotics are indicated in the treatment of Hib disease. Drugs other than ceftriaxone and cefotaxime used to treat Hib infections do not reliably eradicate Hib from the nasopharynx. Hence, if the index patient is under 2 years old and was treated with a regime other than cefotaxime or ceftriaxone, chemoprophylaxis should be given to the index case just before hospital discharge to eradicate nasopharyngeal colonisation with Hib. Complicated cases may require longer therapy.

Dexamethasone may be of benefit in children with Hib meningitis in reducing neurological sequelae, but not mortality, if administered before or concurrently with the first dose of antibiotics.

Epiglottitis is a medical emergency that requires immediate endotracheal intubation or a tracheostomy. Pleural, pericardial or synovial fluid that is infected should be drained.

Precaution, prevention and control

Isolation measures

All cases should be isolated with droplet precautions until 24 hours after starting effective antibiotic therapy.

Contact management

Chemoprophylaxis with rifampicin should be administered as soon as possible to all household contacts of invasive Hib cases when the household includes members that meet any of the following:

• Children under 2 years of age who are not immunised or incompletely immunised against Hib.

• Children under 12 months who have not received their primary series of vaccines.

• Immunocompromised child (regardless of immunisation status).

Chemoprophylaxis is recommended in childcare settings when2 or more cases of invasive Hib disease have occurred within 60 days, and unvaccinated or partially vaccinated children attend the facility. When prophylaxis is indicated, it should be prescribed for all attendees, regardless of age or vaccine status, and for childcare providers.

Healthcare workers without adequate personal protective equipment exposed to the index case’s respiratory secretions prior to completion of 24 hours effective treatment should be offered chemoprophylaxis as well.

Vaccination

Vaccination is the most important strategy for prevention of Hib infection. The recommended series of Hib conjugate vaccines consists of three primary doses given within the first 6 months of life with a booster dose given at 12 to 18 months of age. It can be given in combination with diphtheria, tetanus, acellular pertussis, inactivated poliovirus and hepatitis B either as a pentavalent or hexavalent vaccine.

Notification

Hib is a legally notifiable disease in Singapore.

Who should notify:

• Laboratories

When to notify:

• On laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification for more information.

Notification timeline:

• As soon as possible. No later than 24 hours.

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the number of Hib cases in Singapore.

For more information on Hib, please refer to the World Health Organization website.

For general travel advisory, please refer to Health Advice for Travellers.