Surveillance of diarrhoeal diseases in Thailand.

Bulletin of the World Health Organization, 64 (5): 715-720 (1986) © World Health Organization 1986 Surveillance of diarrhoeal diseases in Thailand K. PHONBOON,' P. KUNASOL,2 T. CHAYANIYAYODHIN,3 & D. SRISOMPORN4 During the period 1978-83, a total of 1 979 118 cases of diarrhoeal diseases were reported to the Ministry of Public Health, Thailand, through the national disease sur- veillance system. The annual incidence steadily increased from about 400 per 100 000 population in 1978 to over 1000 in 1983. A total of3300 deaths from diarrhoeal diseases were reported. The annual number of deaths declined from 911 in 1978 to 370 in 1983, corresponding to a decrease in mortality rate from 2.0 to 0. 7 per 100 000. For acute diarrhoea, the highest incidence rate (608 per 100 000 per annum) was in the central region, that of dysentery (111) was in the northern region, while that offood poisoning (52) was in the northeastern region, enteric fever (45) in the southern region, and cholera (10) in the central region. Recent vital statistics and survey results have indicated that in Thailand diarrhoeal diseases remain an important cause of illness and death (1, 2). In order to provide information for prevention and con- trol activities at national and local levels, the Thai Ministry of Public Health has, since 1970, monitored trends for these diseases. Here, we report data for the period 1978-83 obtained-from the national epidemio- logical surveillance system. MATERIALS AND METHODS Data in the national surveillance system were collected largely through a passive surveillance net- work in each province of the country. After pre- liminary analysis and tabulation at the local level, data were sent to the Ministry of Public Health for further analysis. Details on each case of diarrhoeal disease included the age, sex, place of residence, date of onset, and place of treatment. Five categories of diarrhoeal diseases were distinguished: cholera, enteric fever, food poisoning, dysentery, and acute diarrhoea. Enteric fever included typhoid or para- typhoid infections that were usually diagnosed clinically without culture. Diarrhoea without blood ' Medical Epidemiologist, Division of Epidemiology, Ministry of Public Health, Bangkok 10200, Thailand. Requests for reprints should be sent to this author. 2 Director, Division of Epidemiology, Ministry of Public Health, Thailand. 3 Chief, Evaluation Section, Division of Epidemiology, Ministry of Public Health, Thailand. 4 Senior Officer, Division of Epidemiology, Ministry of Public Health, Thailand. or mucus was usually reported as acute diarrhoea; otherwise, as dysentery. Only cholera was confirmed by culture before reporting. The causative agents of diarrhoeal diseases were generally isolated and identified in provincial hospital laboratories or at a government regional laboratory. Common isolates included Vibrio cholerae, Vibrio parahaemolyticus, Salmonella typhi, Salmonella spp., Shigella spp., enteropatho- genic Escherichia coli, and Entamoeba histolytica. However, these etiological findings were not rou- tinely reported to the national surveillance system. More complicated and expensive laboratory methods for identification of agents such as rotavirus, Campylobacterjejuni, and entero-invasive or entero- toxigenic E. coli have been used only in a few recent studies. RESULTS During the period 1978-83, a total of 1 979 118 cases of diarrhoeal diseases were reported to the Thai Ministry of Public Health through the national sur- veillance system. The annual number of cases increased from 175 411 in 1978 to 537 972 in 1983, and this is reflected in an increase in the annual incidence from approximately 400 per 100 000 popu- lation in 1978 to over 1000 in 1983 (Table 1). The average annual incidence of diarrhoeal diseases re- ported over this period was 694 per 100 000, or approximately 330 000 cases per annum. The number of cases of all categories of diarrhoeal disease increased, except cholera, which fluctuated 4713 -715 K. PHONBOON ET AL. Table 1. Reported number of cases of diarrhoeal diseases, Thailand, 1978-83 AverageNo. of cases annual Disease incidence category 1978 1979 1980 1981 1982 1983 Total (per 100000) Cholera 3923 1498 4288 39 645 1497 11 890 (0.6)° 4 Entericfever 8706 10129 10368 11 326 14105 14901 69535(3.5) 25 Foodpoisoning 8213 12741 18942 21 729 27580 34988 124 193 (6.3) 43 Dysentery 17810 32578 29984 43577 53602 64860 242411 (12.2) 85 Acutediarrhoea 136759 176664 224477 243706 327757 421 726 1 531 089 (77.4) 537 Total 175 411 233 610 288 059 320 377 423 689 537 972 1 979 118 694 Rate (per 100000) 395 514 620 675 874 1088 - - a Figures in parentheses are percentages of the total. from year to year. Acute diarrhoea exhibited the highest average annual incidence (537 per 100 000), followed by that of dysentery (85), food poisoning (43), and enteric fever (25). Cholera had the lowest incidence (4 per 100 000) (Table 1). Over the 6-year study period the majority of cases reported were acute diarrhoea (77.4%), followed by dysentery (12.2%), food poisoning (6.3%o), and enteric fever (3.5%). In contrast, cholera accounted for only 0.6% of cases. am Qm I io JMMJSNJMMJSNJMJ SNJMMJSNJMMJSNJ.MMJSN 1978 1979 1980 1981 1982 1983 Fig. 1. Reported number of cases of acute diarrhoea per month in Thailand, 1978-83. Acute diarrhoea The number of cases of acute diarrhoea followed a regular pattern, with peaks in January and May-July (Fig. 1); these periods accounted for 40.7% of all cases during 1978 to 1983. The age-specific incidence rate for acute diarrhoea was highest in children aged 0-4 years (average 1609 per 100 000 per annum) (Table 2). Cases in this age group accounted for 40.3% (617 490 out of 1 531 089) of the total. Table 2. Average annual age-specific incidence rates (per 100 000) for acute diarrhoea, dysentery, food poisoning, enteric fever, and cholera in Thailand, 1978-83 Average incidence rate Age group Acute Food Enteric (years) diarrhoea Dysentery poisoning fever Cholera 0-4 1609 229 56 15 5 5-9 342 47 47 32 2 10-14 206 30 38 33 1 15-24 288 53 47 29 3 25-44 392 73 61 21 5 45-64 - 93 65 19 9 >65 623° 118 67 16 12 a Figure shown is the incidence rate for those >45 years of age. 716 v w DIARRHOEAL DISEASES IN THAILAND 0 2Z4000- 2000 1000 0 T 1978 1979 198 1981 1 1983 Fig. 2. Reported number of cases of dysentery, food poisoning, and enteric fever per month in Thailand, 1978-83: O =dysentery; + =food poisoning; = enteric fever. Dysentery, food poisoning, and enteric fever Cases of dysentery, food poisoning, and enteric fever showed similar seasonal patterns to that of diar- rhoea. Peaks of food poisoning occurred in April- June, of dysentery in May-July, and of enteric fever in June-August (Fig. 2). For dysentery, the age- specific incidence rate was highest among children aged 0-4 years (average 229 per 100 000 per annum) (Table 2). For food poisoning the mean annual age- specific incidence rates were higher among older adults, the highest rate (67 per 100 000) being among JimJSNJMMJSJMJSNJMMJJsm JSJ"mJSN 1978 1979 1980 1981 1982 1983 Fig. 3. Reported number of cases of cholera per month in Thailand, 1978-83. those aged 65 years or more. From 1978 to 1980 the highest age-specific incidence rate for enteric fever was among children aged 5-9 years, but from 1981 to 1983 the highest rate was among children aged 10-14 years. In the latter age group, the mean annual age- specific incidence rate was 33 per 100 000 (Table 2). Cholera Epidemics of cholera were observed in January 1978, April 1979, and in both March 1980 and 1983. Table 3. Reported deaths from diarrhoeal diseases in Thailand, 1978-83 No. of deaths Disease category 1978 1979 1980 1981 1982 1983 Total Cholera 126 47 85 2 17 41 318 (9.6)° Enteric fever 56 45 27 28 22 21 199 (6.0) Food poisoning 20 20 25 15 20 13 113 (3.4) Dysentery 45 43 26 21 24 20 179 (5.4) Acute diarrhoea 664 539 422 307 284 275 2491 (75.5) Total 911 694 585 373 367 370 3300 Mortality rate (per 100 000) 2.0 1.5 1.3 0.8 0.8 0.7 - a Figures in parentheses are percentages of the total. 717 K. PHONBOON ET AL. Table 4. Average annual age-specific mortality rates (per 100 000) for acute diarrhoea, dysentery, food poisoning, enteric fever, and cholera in Thailand, 1978-83 Mortality rate Age group Acute Food Enteric (years) diarrhoea Dysentery poisoning fever Cholera 0-4 3.35 0.22 0.06 0.05 0.10 5-9 0.65 0.03 0.03 0.08 0.04 10-14 0.20 0.07 0.04 0.07 0.01 15-24 0.15 0.01 0.02 0.09 0.03 25-44 0.24 0.01 0.03 0.07 0.11 45-64 - 0.08 0.05 0.06 0.34 >65 1.61 0.24 0.10 0.11 0.75 a Figure shown is the mortality rate for those >45 years of age. The largest of these was in 1980 with 4288 cases (Fig. 3). The age distribution of cases was the same in epi- demic and non-epidemic years, but the age-specific incidence rates were consistently highest among adults aged 45-64 years (9 per 100 000) and 65 years or over (12 per 100 000). Among children, those aged 04 years had the highest rate (5 per 100 000) (Table 2). Mortality A total of 3300 deaths from diarrhoeal diseases were reported over the study period. Deaths in each disease category, except cholera, decreased, and the annual number of deaths declined from 911 in 1978 to 370 in 1983 (Table 3). Acute diarrhoea was the most common category leading to death. Although cholera accounted for only 0.6% of cases, it contributed to 9.6% of total deaths from diarrhoeal diseases. The average annual mortality rates were 0.9 per 100 000 for acute diarrhoea and 0. 12 per 100 000 for cholera. For acute diarrhoea the highest age-specific mortality rate was among children aged 0-4 years (average 3.35 per 100 000 per annum) (Table 4). Age-specific mor- tality rates for the remaining disease categories were much lower. Geographical distribution The highest mean incidence rate for reported cases of acute diarrhoea occurred in the central region of the country (608 per 100 000 per annum), while that for dysentery was in the northern region (111); for food poisoning the comparable rate was in the north- eastern region (52), and for enteric fever in the south- ern region (45). For cholera, the highest mean rate was reported in the central region (10). DISCUSSION The total number of cases of diarrhoeal diseases re- ported in Thailand has been steadily increasing from 14 981 in 1971, when the national surveillance system was established, to 537 972 in 1983 (3). However, some of this increase may have arisen because of the introduction of improved reporting procedures. Reported cases of diarrhoeal diseases represent only a fraction of the total number in a given year, and the results of a survey in Thailand indicate that, on average, the annual number of episodes of diar- rhoea per child under 5 years of age is two (2). The number of cases of these diseases each year among children of this age group can therefore be estimated as 11 million (number of children aged 04 years = 5 425 846, 1980 Census) (11). If it is then assumed that 607o of cases of diarrhoeal diseases occur in chil- dren of this age group, the total number of cases expected is 18 million, which suggests that the sur- veillance system is insufficiently accurate. Whether over time the number of cases and deaths reported bear a fixed relationship to the actual numbers is dif- ficult to determine. It can only be concluded that the number of cases and deaths reported is increasing, and that this probably includes a greater proportion of actual cases as efforts to improve surveillance become more successful. Reported cases of acute diarrhoea peak in January (cold season) and May-July (rainy season), which is consistent with the results of other studies in Thailand and elsewhere (4-6). The major pathogens are rota- virus and enterotoxigenic E. coli, although both are present throughout the year (4, 5). Similar results have been reported in other countries (7, 8). In epi- demic years the frequency of cholera in Thailand is greater in the first half of the year; however, in Bang- ladesh it is more common in September-November (7). This suggests either differences in the modes and vehicles of transmission of V. cholerae in the two countries or different climatic patterns. The age distribution of both the age-specific inci- dence rates and mortality rates for acute diarrhoea is consistent with previous findings that the youngest age groups are most affected (6-8). In the first few years of life, children probably develop intestinal immunity to the majority of enteropathogens in their environment; in contrast, acute diarrhoea is relatively less frequent in older children and adults, probably due to their acquired protective immunity and better standards of personal hygiene (9). Cases of dysentery show a similar age distribution; however, the other three categories of diarrhoeal 718 DIARRHOEAL DISEASES IN THAILAND disease do not exhibit this age-distribution pattern. For food poisoning and cholera the groups most affected are adults and older adults, while those affected by enteric fever are mostly schoolchildren. Age-related behaviour or life-style, including diet, rather than immunity status, may contribute to these differences. Mortality rates may be underestimated when data from routine surveillance studies are used. However, for 1978 to 1983 a remarkable decrease in the annual number of deaths from diarrhoeal diseases was ob- served in Thailand; the age-specific mortality rate for reported diarrhoeal deaths among children aged 0-4 years (3.8 per 100 000) is approximately ten times lower than that determined from field surveys (39 per 100 000) (2). This indicates that there is a difference in the ratios of estimated:reported cases and esti- mated: reported deaths if calculations are based on the results of community surveys. Mortality report- ing may be more accurate than morbidity reporting. In terms of mortality, diarrhoeal diseases in Thailand appear to have a less severe outcome compared with those reported in other developing countries (10). Since 1980 the National Control of Diarrhoeal Diseases Programme (NCDDP) has been implemen- ted in Thailand (2). The programme, based on the results of surveillance findings, has concentrated on reducing mortality and morbidity among children below 5 years of age. Although mortality from diar- rhoeal diseases has declined in recent years, this is probably not due entirely to the NCDDP. However, it may be an important factor in maintaining the present low mortality rate. ACKNOWLEDGEMENTS The authors wish to thank Dr Bruce G. Weniger, WHO adviser, Field Epidemiology Training Programme, Ministry of Public Health, Bangkok, Thailand, for his assistance in preparing this manuscript. RtSUM1 SURVEILLANCE DES MALADIES DIARRHEIQUES EN THAILANDE Pendant la periode 1978-83, 1 979 118 cas de maladies diarrh6iques, au total, ont ete signal6s a la Division d'Epi- d6miologie du Ministere de la Sante publique de la Thai- lande, par l'interm6diaire du systeme national de surveil- lance des maladies. Les donn6es recueillies comportaient, pour chaque cas, l'age, le sexe, le lieu du domicile, la date du d6but de la maladie et le lieu oii le traitement a 6t6 appliqu6. L'incidence annuelle des maladies diarrh6iques a augment6 regulierement pour passer d'environ 400 pour 100 000 en 1978 a plus de 1000 en 1983. Les maladies diarrh6iques &taient signal6es sous cinq rubriques dont l'incidence moyenne annuelle pour 100 000 6tait: diarrh6es aigues, 537; dysenterie, 85; toxi-infections alimentaires, 43; para- typhoides, 25; et chol6ra, 4. Pour les diarrh6es aigues, il y avait des pics separ6s en janvier et mai-juillet; en ce qui con- cerne l'incidence par age, le maximum s'observait parmi les enfants de 0 a 4 ans (1609 pour 100 000). Les incidences maximales se produisaient en avril-juin pour les toxi- infections alimentaires, en mai-juillet pour la dysenterie et en juin-ao(lt pour les paratyphoides. Le taux d'incidence par age le plus 6lev6 s'observait parmi les enfants de 0 a 4 ans (229) pour la dysenterie; chez les adultes de 65 ans et plus dans le cas des toxi-infections alimentaires et du chol6ra (67 et 12, respectivement), alors qu'en ce qui concerne les para- typhoides cette incidence maximale (33) s'observait chez les 6coliers de 10 a 14 ans. Pendant la p6riode 6tudi6e ici, il a ete signal6 un total de 3300 d6ces dus a l'ensemble des maladies diarrh6iques. Le nombre annuel de d6ces s'est abaiss6 de 911 en 1978 a 370 en 1983, ce qui correspond a une diminution du taux de mortalit6 de 2,0 a 0,7 pour 100 000. Le taux moyen maximal a 6t6 signal6 dans la region centrale du pays pour les cas de diarrh6e aigue (608 pour 100 000), alors qu'il etait rapport6 dans la region septentrionale pour la dysenterie (111), dans la r6gion du nord-est pour les toxi- infections alimentaires (52) et dans la r6gion du sud pour les paratyphoides (45). 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