Hib (Haemophilus influenzae type b) is a bacterial infection that can cause a number of serious illnesses such as pneumonia or meningitis, especially in young children. Hib infections are preventable by vaccination. SEROTYPES In 1930, two major categories of H. influenzae were defined: the unencapsulated strains and the encapsulated strains. Encapsulated strains were classified on the basis of their distinct capsular antigens. There are six generally recognized types of encapsulated H. influenzae: a, b, c, d, e, and f.
Genetic diversity among unencapsulated strains is greater than within the encapsulated group. Unencapsulated strains are termed nontypable (NTHi) because they lack capsular serotypes; however, they can be classified by multilocus sequence typing. The pathogenesis of H. influenzae infections is not completely understood, although the presence of the capsule in encapsulated type b (Hib), a serotype causing conditions such as epiglottitis, is known to be a major factor in virulence. Their capsule allows them to resist phagocytosis and complement-mediated lysis in the nonimmune host.
The unencapsulated strains are almost always less invasive; they can, however, produce an inflammatory response in humans, which can lead to many symptoms. CLINICAL MANIFESTATIONS OF HEAMOPHILUS INFLUENZA TYPE B Symptoms depend on which part of the body is infected which are : a) Meningitis – an infection of the membrane covering the brain. Signs include fever, stiff neck, drowsiness, irritability and refusing food. b) Epiglottitis – inflammation of the flap at the top of the windpipe (epiglottis), which can block a child’s breathing.
Signs can include severe breathing difficulties, fever, restlessness and irritability. c) Pneumonia – lung inflammation. Symptoms include fever, cough, chest pains and breathing problems, such as shortness of breath. d) Septic arthritis – joint infection. Symptoms include joint pain, swelling and reduced mobility of the joint. e) Cellulitis – infection of the tissue under the skin, usually on the face COMPLICATIONS OF THE DISEASE: a) Meningitis b) Pneumonia c) Blindness d) Brain damage e) Paralysis f) Hearing loss g) Death. CONFIRMATORY 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. DESCRIPTIVE EPIDEMIOLOGY OF HEAMOPHILUS INFLUENZA TYPE B * Place * Before vaccines became available, invasive Hib disease was a leading infectious illness among children worldwide.
Hib vaccine is routine in the Americas, most of Europe, and a few countries in Africa and the Middle East. * In the 1990s, frequency decreased remarkably, and even developing countries reported a frequency of only 2-3 cases per 100,000 of the population younger than 5 years. * Overall mortality from Hib meningitis is approximately 5%. Morbidity rates from meningitis, however, are high. * Person * Race * Especially high in certain ethnic groups, including African Americans, American Indians (eg, Alaskan Eskimos, Navajo, Apache, Yakima, Athabaskan), and Australian Aborigines. * Age.
* In general, Hib infections are rare in patients older than 6 years because of the acquisition of secondary immunity; however, immunocompromised individuals remain susceptible. * Hib meningitis primarily affects children younger than 2 years, with a peak frequency in infants aged 6-9 months. * Epiglottitis is most common in children aged 2-7 years but can also occur in adults. * Hib pneumonia typically occurs in children aged 4 months to 4 years. * Hib causes septic arthritis and cellulitis in children younger than 2 years; before the conjugate vaccine became available, * Hib was the leading cause of arthritis in this age group.
* Hib septic arthritis also occurs in adults. * Prior to introduction of the Hib vaccine, Hib was the leading cause of occult bacteremia after Streptococcus pneumoniae in children aged 6-36 months. In the vaccine era, Hib occult bacteremia is rare. * H influenzae otitis media can occur at any age but is most common in children aged 6 months to 6 years. * Sex * Hib disease has no sexual predilection CYCLE OF INFECTION * Agent * Haemophilus influenzae is a gram-negative coccobacillus. Invasive infections are commonly caused by serotype b. * Reservoir * Humans are the only known reservoir for Hib.
* Inlet and outlet * Nose and throat * Mode of transmission * By direct contact with respiratory droplets and discharges from the nose and throat of infected persons, including asymptomatic carriers. * Incubation period * The typical incubation period is not clear, but is probably short, around 2 to 4 days. * The infectious period lasts as long as organisms are present in the nasopharynx. * Cases are probably most infectious in the 3 days before onset of symptoms. * A case can be regarded as non-infectious after 24 hours of treatment with appropriate antimicrobial therapy.
* Susceptible host * Invasive Hib infections are uncommon in children <2 months (because of maternal antibodies) and >5 years old. * The genetic constitution of the host may also be important in susceptibility to infection with Hib. * 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. * 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.
HEAMOPHILUS INFLUENZA TYPE B VACCINATION ( ACTIVE VACCINATION ONLY ) Hib vaccine is recommended for all children under five years old in the U. S. , and it is usually given to infants starting at two months old.
The Hib vaccine can be combined with other vaccines. Some brands of vaccine contain Hib along with other vaccines in a single shot. FOR CHILDREN Children should get a Hib vaccine at: * 2 months * 4 months * 6 months* * 12 through 15 months FOR OLDER CHILDREN AND ADULTS Children over five years old usually do not need Hib vaccine. But some older children or adults with special health conditions should get it. These conditions include sickle cell disease, HIV/AIDS, removal of the spleen, bone marrow transplant, or cancer treatment with drugs.
SIDE EFFECTS OF THE HIB VACCINE * Serious reactions to this vaccine are rare. Mild reactions can include: * A mild temperature * Drowsiness or tiredness * Mild swelling, redness and pain at the injection site * Temporary small lump at the injection site * Irritability or crying – your child may appear generally unsettled. There is a very small risk of a serious allergic reaction to any vaccine. It is important to stay at the clinic where the immunisation was given for 15 minutes after the immunisation. Delay or do NOT give the vaccine if:
* child is under 6 weeks old * child has an illness more serious than a cold * Severe allergic reaction or anaphylaxis occurs after an injection of the Hib vaccine (no furtherHaemophilus influenzae type b immunization should be given to the child) 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.
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. 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.
References * http://www. vaccines. gov/diseases/hib/index. html * http://www. cdc. gov/vaccines/pubs/vis/downloads/vis-hib. pdf * http://www. nhs. uk/conditions/Hib/Pages/Introduction. aspx * http://www. nlm. nih. gov/medlineplus/ency/article/002023. htm * http://www0.health. nsw. gov. au/factsheets/infectious/haemophilusb. html * http://www. betterhealth. vic. gov. au/bhcv2/bhcarticles. nsf/pages/Haemophilus_influenzae_type_b_Hib * http://www0. health. nsw. gov. au/factsheets/guideline/haemflu. html.
* http://www. textbookofbacteriology. net/haemophilus_2. html * http://ideas. health. vic. gov. au/bluebook/haemophilus. asp * http://www. kiddivax. co. za/rsa-pediatric/front/index. jsp? siteCode=RSA-PEDIATRIC&codeRubrique=24 * http://ideas. health. vic. gov. au/bluebook/haemophilus. asp * http://www. hss. gov. yk. ca/pdf/ycdc_invasive_hib. pdf * http://emedicine. medscape. com/article/218271-overview.