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Previous studies of the hemagglutinin (HA) genes of various influenza B virus isolates demonstrated the existence of two antigenically distinct virus lineages represented by B/Victoria/2/87 and B/Yamagata/16/88, respectively. Here, we investigated the antigenic and genetic characteristics of influenza B viruses isolated from children living in Lusaka, Zambia between January and May 1999. Antigenic analysis with chicken antiviral sera showed that all the Zambian isolates had the HA protein belonging to B/Yamagata/16/88-related lineage. Furthermore, phylogenetic analyses of the eight RNA segments performed by using the total or partial nucleotide sequences of the two representative Zambian strains (B/Lusaka/270/99 and B/Lusaka/432/99) as well as the previously reported sequences suggested that the Zambian viruses are closely related to the recently circulating reassortants represented by B/Shiga/T30/98 and B/Yamanashi/166/98 which acquired the genes coding for three polymerase proteins (PB2, PB1, and PA), HA, nucleoprotein, and matrix protein from a B/Yamagata/16/88-like parent and the gene encoding nonstructural proteins (NS1 and NS2) from a B/Guandong/8/93-like parent.

Epidemiological research on respiratory syncytial virus (RSV) infections in children was carried out at the Virology Laboratory, University Teaching Hospital (UTH), in Lusaka, Zambia, from January-December 1996. Specimens including 736 nasal washings and 2424 throat swabs were collected from children with acute respiratory infections (ARI) and tested for RSV by enzyme immunoassay and by virus isolation. RSV was isolated in 62 (4.1%) of 1496 throat swabs collected from March to September and was detected in 99 (16.3%) of 609 nasal washings from March to November. The average RSV isolation rate was 2.6% and the average RSV detection rate was 13.5%. The highest RSV isolation (8.1%) and detection (30.5%) rates were in June 1996. RSV antibody in the 278 serum specimens collected from Zambian children, who were hospitalized in the paediatric ward, UTH, was detected using a standard neutralization test. The antibody positive rate was 60-80% in children > 4 years. It is evident that RSV is one of the main causal agents of ARI in children in Zambia.

Laboratory diagnosis of measles infection is rarely performed in developing countries and tends to depend on clinical symptoms alone. We evaluated detection of immunoglobulin M (IgM) antibodies for confirmation of acute measles infection in Zambia. In 149 hospitalized children with clinical diagnosis of measles, IgM antibodies were detected in 88.6% (132/149). The IgM-positive rate increased with time after onset of skin rash and all samples were positive after 4 days. In addition to IgM antibody test, virus isolations from throat swabs using B95a cells were also performed. These were positive in only 20.9% (14/67), and both IgM and virus isolation in combination increased the positive rate to 92.5% (62/67). Vaccinated children had higher neutralizing (Nt) antibody responses and, among IgM-negative patients, all 4 vaccinated children had high Nt antibodies while all 10 unvaccinated children had negative or low Nt results. The IgM antibody test was proved to be a sensitive method for laboratory confirmation of measles virus infection in developing countries.

A viral aetiological and epidemiological study of acute respiratory infections (ARI) in children was carried out in Lusaka, Zambia between June 1993 and September 1995. A total of 3,760 throat swab specimens were collected for virus isolation from children under 5 years of age who had ARI and were attending three health centres in Lusaka. Between June and November 1993, 52 cases of the influenza A/H3N2 viruses were isolated. Between May and July 1994, 34 influenza B cases were isolated. In 1995, one A/H3N2 influenza virus was isolated in January and then the same type of influenza virus was isolated from 55 samples between June and August. The isolation rate of influenza virus was highest at 14.3% (20/139) in August 1993, at 15.1% (18/119) in June 1994 and at 25.4% (43/169) in July 1995. This is the first report of a consecutive study of influenza virus infections in Zambia and the results reveal that influenza virus infections are one of the most important pathogens of ARI in children in the cool, dry season (June-August) in this country.

The prevalence of hepatitis B virus (HBV) markers was studied in pregnant women attending antenatal clinics in Zambia. A total of 2,098 pregnant women were recruited into the study at three urban health centres in Lusaka, the capital city and four district hospitals in rural areas of different provinces of Zambia. The overall prevalence of HBsAg was 6.5% (137/2,098), and HBeAg was present in 16.1% (22/137) of those positive for HBsAg. Antibody positive rate (HBsAb and/or HBcAb) was 51.3% in randomly selected HBsAg negative samples. HBsAg positive rate varied between 3.3% and 13.6% in each study sites. Prevalence for both HBsAg and antibodies to HBV were significantly higher in rural areas (district hospitals) than in urban areas (urban health centres in Lusaka). These data show that although HBV is endemic in Zambia, the prevalence varies from region to region.

A 2-year hospital-based survey of measles infections were carried out at the University Teaching Hospital (UTH) in Lusaka, Zambia from January 1992 to December 1993. During this period, a total of 1066 children with a clinical diagnosis of measles were admitted to the paediatric isolation ward at UTH. Measles cases were seen throughout both 1992 and 1993. However, there was a peak from September to December, 1992. The number of cases decreased with age, and 370 (34.7%) were under 1 year old. It is noteworthy that 203 (19.0%) were less than the 9 months of age which is the recommended time for measles vaccination in Zambia. The overall case fatality rate was 12.6%, and was higher in children aged 0-3 years (14.3%) than in those aged 4 years and above (6.7%). Measles vaccination status could be checked from the child's immunization card for 343 measles cases over 9 months of age, 118 (34.4%) of these having previously received measles vaccine. Vaccinated children had a significantly lower case fatality rate (6.4%) than the unvaccinated group (17.0%). This suggests that while measles vaccine cannot prevent infection, it can reduce the severity of infection.

There was an outbreak of "a mysterious disease" at a Zambian school dormitory in September, 1993. Investigation with questionnaire and collection of throat swab specimens for virus isolation were carried out on 46 patients to identify the causative agent. In this outbreak, most of the patients showed similar symptoms such as fever, headache, sore throat, cough, etc. The disease had spread to all dormitories within a couple of days after the onset of the first cases. From these patients, 13 influenza viruses A/H3N2 were isolated on MDCK cell line. This was a first ever confirmed outbreak of influenza virus infection in Zambia.

The clinical and epidemiological aspects of rotavirus diarrhoea were studied in hospitalized children with acute diarrhoea in Lusaka, Zambia. Two hundred and fifty-six (24.0%) of 1069 children admitted to the study were shedding rotavirus. The rotavirus-positive rate was highest in children less than 1 year of age (37.0%) and it was also high in those less than 6 months old. Rotavirus diarrhoea was seen throughout the year with a higher rotavirus-positive rate in the dry season. In rotavirus-positive diarrhoea patients, more children were dehydrated (82.4%) than in the rotavirus-negative group (56.2%). Rotavirus infection was more common in the children with normal nutritional status (27.6%, 162/588) than in those with malnutrition (19.3%, 93/482). The associated case fatality rate in the rotavirus-positive group was 6.4%, significantly less than in the rotavirus-negative group (OR 0.44, 95% CI 0.24-0.79), and mortality cases were seen only in children less than 2 years old.