DENGUE HAEMORRHAGIC FEVER (Incidence and mortality)

Dr Tan Eng Liang asked the Minister for Health and Home Affairs (a) if he is aware that the University authority has reported a total of about 370 notified cases of Dengue Haemorrhagic Fever (DHF) with at least 10 deaths for the period April to July 1973, whereas his Ministry has not officially reported any outbreak and has only published four deaths; (b) why is there such a discrepancy; (c) what are the actual figures, both of incidence and mortality; and (d) in view of the seriousness of this disease, if he will consider making DHF a notifiable disease by law as in the case of malaria.

The Minister for Health and Home Affairs (Mr Chua Sian Chin): Mr Speaker, Sir, the answer to sub-question (a) is yes. The figures on the number of cases and deaths were from a feature article published by a Senior Lecturer of the Department of Bacteriology, University of Singapore. The Department of Bacteriology undertakes the laboratory diagnosis of Dengue Haemorrhagic Fever. This is done by way of tests on blood samples sent from the hospitals and out-patient dispensaries from patients suspected to be suffering from Dengue Haemorrhagic Fever. To be certain, the tests are required to be repeated after two to four weeks. It should, however, be noted that the figures from the Department were incomplete as not all suspected cases had their blood sent to the laboratory and a second blood specimen could not always be obtained.

The failure to make an official announcement on the outbreak of Dengue Haemorrhagic Fever was due to lack of information initially and later by a lack of co-ordination between the Ministry of Health and the Ministry of the Environment. The initial lack of information was due to the slow buildup of cases over the average "background" of cases. Since the disease can only be definitively diagnosed by laboratory tests which require two blood specimens taken after an interval of two to four weeks, the outbreak was not evident until a lapse of time. It must be remembered that Dengue Haemorrhagic Fever is endemic in Singapore and cases occur throughout the year as the figures show since 1966.

The reports of cases occurring in the hospitals were sent, as is the normal practice, directly to the Epidemiology Unit of the Ministry of the Environment, which should have been the official source of information when it became evident that an outbreak had occurred. The absence of an official announcement is because of poor communication and co-ordination between the Ministry of Health and the Ministry of the Environment. The Ministry of the Environment had taken over the responsibility of public health, which included the Epidemiology Unit from the Ministry of Health when the Ministry of the Environment was established in September last year. This deficiency in co-ordination, however, will be put right by regular meetings of a Co-ordination Committee on Epidemic Diseases which has been formed comprising officials from the two Ministries.

In answer to sub-question (b), regarding the discrepancies between the figures purported to be reported by the various authorities, the explanation is as follows. Firstly, no official release on the number of cases and deaths was made by the Ministry of Health. This was because the reports from the hospitals were presumptive and could have included other fevers such as influenza, encephalitis, while the laboratory reports were retrospective. Secondly, figures quoted in the press as coming from the Ministry of Health were probably obtained from unofficial sources. In answer to sub-question (c), regarding the actual figures, both of incidence and mortality, the total numbers for the period April to July 1973 were 207 cases and 20 deaths. These figures were reported by the Epidemiology Unit of the Ministry of the Environment and should again be regarded as presumptive. Without an autopsy it could not be absolutely certain that all the deaths were due to Dengue Haemorrhagic Fever.

In answer to sub-question (d), Dengue Haemorrhagic Fever is not a notifiable disease. It is, however, by administrative directive made notifiable within the Ministry's services. This was for the purpose of identifying areas of Aedes mosquito breeding and for assessing the effectiveness of mosquito eradication measures over a period of time. Generally, the object of making a disease notifiable is one or a combination of the following reasons:

(i) in the case of a dangerous infectious disease where immediate steps are required to control the disease. This is required by international agreement. The purpose is to alert the international community to take appropriate steps against the disease. These are mainly steps in sanitation and in protective measures. In the case of Dengue Haemorrhagic Fever, the only effective measure against the disease is the eradication of the Aedes mosquito vectors. There are no protective measures such as immunisation. Further, unlike Malaria, personal protection by sleeping under mosquito nets, using mosquito repellents are of limited value, as the mosquitoes tend to be "afternoon biters".

(ii) for epidemiology studies - mainly the collection and tabulation of figures and statistics. In a limited way the administrative instruction for notification of the disease by the Government institutions is for this purpose.

Information is useful for a comprehensive long-term prevention programme of the disease. In the case of dengue fever, there is only one action to be taken, that is, the eradication of mosquito breeding. This is a continuous and continuing campaign taken whether or not the disease is present or peaking. The experts in my Ministry are not yet satisfied that this disease is so easily and quickly identifiable as to make notification in law useful for immediate counter action.