Dengue/DHF

Dengue Bulletin Volume 22, December-1998

Epidemiology of Dengue Haemorrhagic Fever in Myanmar, 1991-1998

By
Khin Mon Mon, Saw Lwin, Soe Aung and Thar Tun Kyaw
Vector Borne Disease Control Project, Department of Health
Yangon, Myanmar

Introduction

Myanmar is situated at 92º - 102º east longitude and 10º - 28º north latitude. The population of the country is 46.4 million. Myanmar is divided into 7 states and 7 divisions for administrative purposes. The states/divisions have been sub-divided into 63 districts and 324 townships. Myanmar, being located in the tropical zone, has a relatively high temperature and humidity, which are favourable conditions for the perpetuation of Ae. aegypti.

Sporadic cases of clinically-recognizeable DHF were first noticed in 1969 in Yangon Children’s Hospital which was followed by the first epidemic in Yangon in 1970⁽¹⁾.From 1970 to1995, a total of 83 381 cases and 3242 deaths, with a case fatality rate (CFR) of 3.9%, were recorded. The incidence of DHF increased over the two decades (1970-1980) and (1981-1991). DHF spread from Yangon to other states and divisions beginning 1975 but two states (Chin and Kayah) remained unaffected up to 1997. This report covers the period 1991-1998 in which certain changes have taken place.

Epidemiology

DHF incidence and trend analysis

The yearly DHF morbidity and mortality data with CFR are shown in Table 1. The trend of DHF cases is on the rise with (b=+253) based upon the absolute number of cases from 1991 to 1998. The case fatality rate has shown a downward trend with (b=-0.16).

Table 1. Yearly DHF morbidity and mortality - Myanmar, 1991-1998

* Provisional data

Seasonal distribution

In Yangon division, DHF transmission occurs throughout the year. But in other states and divisions the cases start to happen from May. The number rises during the rainy season, i.e. the second week of May to the second week of October. After that, the cases decline to around zero in the states and divisions and to less than 100 in Yangon division. Water storage practices in Yangon division provide year-round breeding opportunities for the vector, whereas in other states and divisions breeding sites get established in the rainy season only, which may be the reason for the high transmission at that time.

Distribution of cases by states and divisions

According to the status report of DHF in Myanmar for 1970-1995, Yangon division contributed 47.8% of the cases while Bago, Mon, Mandalay and Magwe contributed 42.5%. A low level of contribution, i.e. 14.8%, was from Ayeyarwaddy, Kayin, Sagaing, Rakhine, Tanintharyi and Kachin. ShanState contributed the least proportion, i.e. 0.9%.

The distribution of DHF cases during 1996-1998 among different states and divisions is shown in Table 2. Kayah state reported its first DHF case in 1998. All four cases were serologically,confirmed, thus Kayah joined the list of DHF endemic states. Ayeyarwaddy division joined the `moderate contribution’ category from the low category level in previous years. Shan state attained the ‘low contribution’ category from the ‘least contribution’ category because of epidemics in its southern parts in 1998.

Table 2. Percentage contribution of cases by states and divisions (1996-1998)

Age-group-wise distribution

The age-wise break-up of DHF cases is shown in Figure 1 and Table 3. It appears that the worst affected age-group is 5-9 years, followed by 0-4 and 10-14 years. The least affected one is 15 years and above.

Table 3. Proportion (percentage) of age-group-wise distribution of DHF morbidity, Yangon division, 1994-1998

According to Table 3 above, the under-5-year age-group was more affected in the non-epidemic years (1996 and 1997). Almost an equal proportion of cases occurred among the under-5-year and 5-9-year age-groups in the epidemic years (1994 and 1998). Morbidity among the 15-year-plus age-group was found in both the epidemic years.

Discussion and conclusion

DHF is endemic in Myanmar with a 3-4 year epidemic cycle. The incidence has been increasing over the past 20 years and the upward trend is still continuing. The provisional number of cases in 1998 was the highest ever recorded in Myanmar but the mortality was not so high as in 1994 (See Table 1).

The CFR in Myanmar is apparently higher than in other neighbouring countries such as Thailand. It may be due to the fact that the cases reported were only hospital cases which were DHF Grade II and above. Grade I cases were not admitted and were therefore not included in the case report. So the denominator of CFR is rather less than actual and it accentuates the result.

Regarding the age-group-wise distribution, the under-5 and primary school-going age-group suffered in almost the same porportion. Therefore, the National Health Committee highligthed the school health programme and the IMCI (Integrated Management of Childhood illness) strategy was also encouraged.

Reference

1.      Tun Tun Aung, Soe Win and Soe Aung. Status report on epidemiology of dengue/eengue haemorrhagic fever in Myanmar, 1995. Dengue Bulletin, 1996, 20:41-45.