Spectrum and Burden of Severe Haemophilus Influenzae Type B Diseases in Asia

Article excerpt

Voir page 884 le resume en francais. En la pagina 884 figura un resumen en espanol.

Introduction

Only a decade ago, Haemophilus influenzae type b (Hib) diseases devastated children in the USA as much as poliomyelitis had during the peak epidemic years of the early 1950s (1). Conjugate vaccines are now changing the picture entirely (2), but they are not utilized globally.

In Asia one of the obstacles to their use is the generally held view that Hib diseases are uncommon (3-8). This impression can be only partly explained by a questionable ability to culture H. influenzae (9). Reference is often made to Hong Kong Special Administrative Region of China, where no Hib strains were found among 0-4-year-old Chinese children (621 throat swabs), as opposed to 1.3% of Vietnamese children (10). Ethnic group was the only predictor suggesting Hib carriage, and this finding may explain the low incidence of Hib disease in Hong Kong, where different populations often live in rather dissimilar conditions (6-8).

Data from Asian populations living elsewhere are controversial. In Sydney, Australia, Hib disease is uncommon among Chinese and Vietnamese populations (11). In California, the risk of Hib disease among Hispanic children used to be slightly lower, and in Asian children significantly (P [is less than] 0.001) lower, than that among Caucasian and Black populations (12). However, a high incidence of Hib disease has been observed among Vietnamese refugees in Hong Kong Special Administrative Region of China (7), and among Bangladeshi, Indian, and Pakistani populations in the United Kingdom (13). One may argue that crowding and better surveillance may have contributed to the findings, but whatever the reasons, even the views of experts differ considerably.

This study attempts to look at a complex issue in its entirety, i.e not just meningitis (14), which occupies only a part of the Hib disease spectrum. It was sought to determine whether all of Asia really does enjoy a low incidence of severe Hib diseases, and what the global burden is for these life-threatening infections against which effective vaccines are already available.

Methods

A detailed literature search was undertaken to trace existing information on invasive Hib diseases in Asia. As defined by the World Bank (15), Asia was taken to be a geographical entity that extends from the Mediterranean Sea in the west to the Pacific Ocean in the east, including the Middle East and Japan but not Turkey, Russian Federation, or Papua New Guinea.

The great majority of the data used here were obtained from the published literature, but some originated from international scientific meetings. A considerable amount of information was published in languages other than English. Inclusion of all reports, irrespective of language, was deemed essential to increase precision and perhaps to reduce systematic errors (16, 17). Because bacteriological methods have improved considerably over the last 30 years or so, earlier studies were not included.

It was expected that the quality of studies would vary, and that the majority of surveys would be retrospective; prospective studies were thus a search priority. The analysis particularly focused on incidence data obtained from population studies, rather than from official reports, which tend to be unreliable. Attention was paid not only to children under 5 years of age -- who account for the majority of cases of Hib disease (1, 18) -- but to all age groups and the entire spectrum of manifestations of Hib. A total of more than 100 reports in six languages from 25 countries throughout the continent were scrutinized.

Demographic calculations were made using World Bank data (15). Actual numbers of cases were calculated from the incidences.

Results

Clinical manifestations

Meningitis. As expected, bacterial meningitis captured the most attention. …