Dengue/DHF

Dengue Bulletin Volume 21, December-1997

Dengue Control through Schoolchildren in Thailand

By
Dr Yongyuth Wangroongsarb
Vector-Borne Disease Control Programme,
Department of Communicable Disease Control,
Ministry of Public Health
Nonthaburi11000, Thailand
Fax 66-2-965-9007

Introduction

Dengue haemorrhagic fever, a severe form of classical dengue, is one of the tropical diseases transmitted by Aedesmosquito. The disease has worldwide distribution, but is more prevalent in the regions of south-east Asia, western and eastern Pacific islands, the Caribbean and Latin America^(1,2). It is also stated that DHF is a new, emerging or re-emerging infectious disease, which is threatening people living in many regions^(3,4).In Thailand, for almost 50 years after the first recognition of the disease in 1949, DHF has spread across the country. It is considered an endemic disease in certain areas⁽⁵⁾. With the availability now of better medical and health care facilities to communities, there has been a sharp decrease in the death and case fatality rates during the past few decades; however, the morbidity rate seems to remain rather stable.

Epidemiological situation

Morbidity and mortality

After DHF was first recognized in 1949 at Bangkok, more than 1500 cases were reported during 1950-1957^(1,6). Later in 1958, there was an outbreak of DHF in Bangkok and other surrounding provinces^(1,7,8). Since then, the number of reported cases has been gradually increasing over time, from 2158 cases in 1958 to 7663 cases in 1965. During 1958-1967, the disease occurrence was confined only to Bangkok and other big cities, but later in 1978, the disease spread across the country in urban areas and then to rural areas with a larger number of cases – 12 547 in 1978 to 80 076 in 1985. In 1987, the cases touched a high of 174 285, which was the largest number ever recorded⁽⁷⁾. Since 1990, the number of the reported cases has been declining every year, approximately 40 000-60 000 cases a year (Fig.1).

Table 1. Morbidity, mortality and case fatality rates of DHF in Thailand, 1958-1996.

In 1958, 300 persons died of DHF (1.23 deaths/100 000). Although the number of deaths due to DHF has fluctuated during the past few decades, the mortality rate seems to be on the decrease during the same period – from 1.19/100 000 in 1959 to 0.19/100 000 in 1996. Similar is the trend in the case fatality rate – down from 13.9% in 1958 to 0.31% in 1996 (Table 1). This seems to be due to improvements in medical care and services as well as better accessibility to medical services and health facilities of people in communities. Nevertheless, the case fatality rate in the past few years seems to be rather stable.

Seasonal variation

DF/DHF occurs mostly in the rainy season (from May to October) which coincides with the reopening of schools for new sessions^(1,9). The peak of the disease outbreak usually is reached in June and July (see Fig. 2). It is noticed that man-made containers are the most potential Aedes breeding places commonly found in the rainy season, and shortage of water supply at some periods of time had resulted in a significant increase in the number of water containers even though piped water supply was available⁽¹⁰⁾. Moreover, schools and households in villages, with high disease prevalence, had a higher number of water containers that resulted in more vector populations⁽¹¹⁾.

Age distribution

DHF cases are mostly found in the age group 5-9 years. Annually, the number of cases in the age group of 5-14 years accounts for 70-75% of total reported cases (Fig. 3). The average morbidity rate during the past five years (1987-1991)

among the 5-14-year-old children was extremely high – 447.8 cases/100 000 a year. This number is about 3-4 times higher than that of all age groups^(7,9). It has been noticed that the age distribution of the disease has shifted to the higher age group during the past decade, from 0-9 years to 5-14 years (Fig. 3).

Conventional methods of dengue prevention and control

Currently, the dengue programme is an integrated programme which has a community-based prevention and control approach. It is now recognized that without community participation, dengue control is neither achieveable nor sustainable^(13,14). Several models of dengue control through the community participation approach have been studied during the past decades^(15,16). Health volunteers like village health volunteers, village leaders, village councils, monks, teachers, elderly women and other local prime movers in villages were encouraged to participate in the programme. Periodic clean-up campaigns were organized by health personnel to effect vector source reduction and other environmental modifications. Social mobilization by utilizing the mass media, community talks and public relations, and various other strategies were used to initiate and encourage communities to participate in the search, elimination and destruction of the aquatic foci which were potential larval breeding sites. Incentives and rewards were also provided to volunteers and community members to promote their participation and to help them develop health education and health communication. However, these model also did not prove viable due to inconsistency and non-sustainability of their participation in dengue control activities. This could have been due to the reason that the suitability of the community participation approach was dependent on various socioeconomic, cultural and political features in the community. A small and well-organized community, which is culturally and economically more homo-genous, is more suitable for community initiative than the rapidly growing, socially complex and multicultural urban communities⁽¹⁷⁾. It is well recognized that dengue control activities must be integrated with other health sectors and the community. Dengue control in primary schools is another development model which uses primary school children as volunteers for vector control in schools and communities. This school-based approach seems to be working success-fully in Thailand after five years of programme implementation.

Dengue control through schoolchildren

According to epidemiological analysis, the disease victims are young school children aged below 15 years. They are mostly primary school children (grades 1-6) and secondary schoolchildren (grades 7-9). The peak of the disease usually occurs in June and July, the same period as the schools commence. Actually, the disease is transmitted by Aedes mosquitoes which are day-time biting vectors. Thus, it is argued that the disease transmission might be happening in school areas^(5,7,9,18). Several research studies on model development of DHF prevention by the community-based approach focusing on primary schools had been conducted in several provinces^(15.19,20). In these studies, schoolchildren were educated about dengue, its transmission and prevention. They were initiated and encouraged as health volunteers to participate in vector survey and vector control in their schools while local health workers technically supervized and promptly supported them with supplies. The outcome of this strategic approach, in terms of disease prevention, was satisfactorily successful as compared with other conventional approaches. Aedes larval indices were reduced by 60-80% in comparison with the results obtained from conventional models^(15,19). It was also found that school-children were more effective than village volunteers, particularly in urban commu-nities⁽¹⁹⁾. These studies substantially encouraged the Ministry of Public Health to revise the control strategies. Finally, in cooperation with the Ministry of Education, the Ministry of Public Health decided to establish a joint project for national dengue campaign in primary schools, which started in 1992.