Thailand

00000000Before the first large outbreak of DHF/DSS in 1958, approximately 50 to 100 cases diagnosed as "influenza with haemorrhage" were included in the hospital records of Siriraj Hospital in Bangkok(36). After the 1958 outbreak in Bangkok and its suburbs, the disease spread to adjacent provinces in the Central region in 1961(37). In 1964, a major outbreak occurred in big cities in northern and north-eastern Thailand(38). The highest record of DHF/DSS (5403 cases with 216 deaths) was reported in 1964 from Bangkok. Since 1968, there have been reports of the disease from almost every province of the country. During the first ten-year period (1958 - 1967), epidemics occurred in alternate years with peaks during the rainy seasons. Even in low epidemic years, the number of patients increased yearly except in 1986. The number of cases recorded was 69 597 in 1984, 80 076 in 1985, 27 837 in 1986 and 174 285 (with 1007 deaths) in 1987(12), which latter was the highest figure ever reported in the WHO South-East Asian region. The case fatality rate was approximately ten per cent in 1958, but gradually decreased to below one per cent by 1980(39).

00000000After 1968, the epidemic pattern of alternate years changed and became irregular for the whole country(31). Case records in Bangkok remained high but did not exceed the 1964 number and followed the country-wide pattern. Since 1973, the number of patients in the north-eastern part of the country has increased significantly every year, and now comprises almost 50 per cent of the cases for the whole country(40). In the early epidemic years, the number of cases in the dry seasons (November to March) was very low (below 100 cases per month), with most reported cases occurring in Bangkok. In other provinces the number of cases was less than ten per month during the dry-cool season (November to February).

00000000Between December and January from 1979 - 1985, the reported number of DHF cases was higher than 100 per province per month in four-five provinces of the central and north-eastern regions. The total reported number of patients in the dry-cool season was, therefore, more than 500 cases per month between November and February. For the whole country, case records reached 2345 in December 1984, and 1859 in January 1985(39,40). This changing pattern is under investigation.

00000000In Thailand, Aedes aegypti is the main vector of DHF(41). Isolation of dengue virus from Aedes albopictus was also reported when a small outbreak of DHF occurred in the insular setting of Koh Samui in southern Thailand(42).
Surveillance of DHF cases in Thailand, which has a mainly clinical basis, has been conducted for several years. For surveillance purposes, all cases with undifferentiated fever. Pyrexia of unknown aetiology, or fever persisting for about five to seven days in which common cold and upper respiratory tract infection have been excluded, have to be notified.

00000000Serological examination has revealed that 40 - 50 per cent of these cases are dengue virus infection(43). In this regard, the over-reporting and under-reporting of DHF cases in Thailand seem to balance.

00000000Virus isolation from patients admitted to Bangkok Children's Hospital has been performed almost every year at AFRIMS (formerly called SEATO Medical Research Laboratory). The analysed results are shown in Figures 2 and 3 in chapter 1.1(44,45). It should be pointed out that DEN-2 has predominated every year, while DEN-1 and DEN-4 have appeared during alternate years.