Non-type bHaemophilus influenzae disease: clinical and epidemiologic characteristics in the Haemophilus influenzae type b vaccine era

http://www.pidj.com/article.asp?ISSN=0891-3668&VOL=20&ISS=3&PAGE=300

Non-type bHaemophilus influenzae disease: clinical and epidemiologic characteristics in the Haemophilus influenzae type b vaccine era

PAUL T. HEATH, FRACP*; ROBERT BOOY, FRACP; HELEN J. AZZOPARDI, FIBMS; MARY P. E. SLACK, FRCPATH; JERRY FOGARTY, FFPHMI; ANNE C. MOLONEY, FRCPATH; MARY E. RAMSAY, MFPHM; E. RICHARD MOXON, FRCP

From the Oxford Vaccine Group (PTH, ERM) and the Public Health Laboratory Service Haemophilus Reference Laboratory, John Radcliffe Hospital (HJA, MPES), Oxford, UK; the Department of Child Health, Queen Mary, University of London (RB), and the Communicable Disease Surveillance Centre, Colindale (MER), London, UK; and the Department of Public Health, Western Health Board, Galway (JF); Regional Pathology Laboratory, Waterford Regional Hospital, Waterford (ACM), Republic of Ireland.

THE PEDIATRIC INFECTIOUS DISEASE JOURNAL 2001;20:300-305

Background. As a result of the decline in Haemophilus influenzae type b (Hib) disease caused by the widespread use of conjugate vaccines, non-type b H. influenzae will become a more important cause of H. influenzae (Hi) disease. Characterization of the clinical and epidemiologic features of non-b Hi disease is needed in the Hib vaccine era.

Methods. A prospective active surveillance study of invasive Hi disease involving pediatricians in the United Kingdom and Republic of Ireland. For the first phase of the study (October 1, 1992, to October 31, 1995) pediatricians were asked to report any child who had invasive Hi disease and who had received Hib conjugate vaccine. For the second phase of the study (November 1, 1995. To December 31, 1998) pediatricians were asked to report any child with invasive Hi disease regardless of vaccination status.

Results. During the study period 102 cases of invasive non-type b Hi disease and 106 cases of invasive Hib disease were reported in children who had been fully vaccinated against Hib. Children with non-type b disease were younger (16 vs. 22 months of age, P = 0.08), less likely to have meningitis and epiglottitis (P 0.001) and more likely to have pneumonia and bacteremia (P 0.001) than children with type b disease. For the last 2 years of the study invasive Hi disease occurring in a fully vaccinated child was more likely to be caused by a non-b strain than by a type b strain (58 vs. 38). In 1998 the incidence of non type-b Hi disease in all children <5 years of age in the UK was 1.3/100 000 as compared with an incidence of Hib disease of 0.6/100 000. The majority (88%) of non-b strains isolated in children were nontypable strains.

Conclusions. Non-b Hi is a rare cause of disease in children, but in the Hib vaccine era it has become more common than type b as a cause of Hi disease in fully vaccinated children.

Key words: Haemophilus influenzae; vaccines; epidemiology

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