We propose a new approach for the analysis of seroprecvalence data. The seroprevalence date on Toxoplasma gondii infection published in 1997 at Kobe University Hospital were analyzed, with a simple mathematical model, Y = exp (-λt), where Y, λ, and t represent the percentage of seronegative people, annual infection rate and age, respectively. After calculating the mean annual infection rate (MAIR) on the basis of the above data, we determined the relationship between MAIR and the year of birth of the female participants in the study. Our present study indicates that MAIR for women born between 1940 and 1960 decreased over the years, and that infection rates correlated with the year of birth. Moreover, assuming that the historically declining trends of MAIR mainly reflect infection rate changes in childhood, we created a simulation of MAIR for the age under 5 years. This simulation demonstrated that MAIR for the age under 5 years decreased from around 4% for females born in 1940, to about 1% for those born in 1960. For women born after 1960, it implied that infection rates might have been cyclically fluctuating from 0% to 1%, with an approximate 10-year interval. Our analyses imply periodic outbreaks of T gondii infection among young children in Hyogo prefecture. In Japan, it is difficult to make a sophisticated statistical analysis of seroprevalence of T. gondii mainly due to the lack of available data. Despite simplicity of our new approach, we believe the approach will be useful to grasp the current and the past situations of T gondii infection even without enough data.

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V cholerae O1 isolated in Vietnam in 1995 and 2000 were characterized. Most of the isolates in 2000 showed moderate resistance to tetracycline and chloramphenicol, and strong resistance to sulfamethoxazoltrimethoprim. The susceptibilities to ampicillin, erythromycin, nalidixic acid and ofloxacin were not very different from those of the isolates in 1995. V cholerae O1 strains showing this kind of drug susceptibility pattern are unique to the seventh cholera pandemic, and they have become widely distributed in Southeast Asian countries. Genetic analysis of the strains from Vietnam by arbitrarily primed polymerase chain reaction suggested that they might be clonal derivatives. In prophage type, 6 of 20 strains (30%) in 1995 and 1 of 24 strains (4%) in 2000 belonged to Ubol type. Considering the current spreading of V cholerae O1 with such unique susceptibility to the drugs, we recommend careful monitoring of the drug susceptibility of V cholerae O1 throughout the world.

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Drug susceptibility of Staphylococcus aureus has been examined in the past 9 years to monitor the appearance of drug resistant strains especially methicillin resistant S. aureus (MRSA). The pattern of drug susceptibility has been relatively constant, but S. aureus is gradually becoming resistant to ampicillin. One MRSA was isolated in 1996 from the nasal vestibulum of a non-infected patient at Mahosot Hospital but not isolated thereafter. In 2001, 2 strains of MRSA which belonged to different clones were first isolated from the infection foci of patients. One was isolated from Setthathirath Hospital, where many Japanese staff have been dispatched since 2000. Careful monitoring and epidemiological studies of MRSA are recommended.

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Two new black-fly species, Simulium maenoi sp. nov. and S. choochotei sp. nov. are described, based on the reared females, reared males, pupae and mature larvae collected in Chiang Mai Province, northern Thailand. In addition, the male, pupa and mature larva of S. digrammicum Edwards, 1928, originally described from Peninsular Malaysia and Thailand, are described for the first time. All these three species are assigned to the griseifrons species-group within Simulium (Simulium) Latreille s. str.

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One hundred and eighty-one patients with acute diarrhoea attending the gastroenteritis ward of Sukra Raj Tropical and Infectious Disease Hospital (STIDH) were investigated during the early monsoon, April to May 2001. Bacterial pathogens were isolated in 33% of the patients. Enteropathogenic Escherichia coli was isolated in 8.28%, Shigella species in 13.25% and Vibrio cholerae 01 in 1.1% of the patients. Mixed infections with bacterial pathogens, helminths and protozoan parasites were commonly observed in the study. Trichuris trichiuria was detected in 27.6%, hookworms in 12.7% and Ascaris lumbricoides in 11.04%. Entamoeba histolyticaldispar and Giardia lamblia were observed in 12.7% and 7.73% of the patients, respectively. A large number of Cryptosporidium (7.73%) and Cyclospora species (3.86%) usually present in immunocompromised patients were also detected in acute diarrhoeal cases. The results showed that a wide range of bacterial pathogens was isolated from the inhabitants of Kathmandu, Nepal prior to the monsoon. These findings indicate that the bacterial pathogens, especially diarrhoeaginic E. coli and Shigella, and protozoan parasites, need to be given additional attention in the diagnosis and treatment of acute diarrhoea.

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