ISSN 1020-6256

May 29, 1998

COMMUNICABLE DISEASES FEEDBACK REPORT

Reporting Period: Epidemiologic weeks 1- 12, 1998

A Review of Selected Communicable Diseases

Dengue Fever

During the reporting period under review (epidemiologic weeks 1-12, January 4 through March 28, 1998), 914 cases of dengue fever were notified to CAREC’s Epidemiology Division. This figure represents a near three-fold increase over the 246 cases recorded during the corresponding period of 1997 (Table 1). This significant increase in the overall reported 1998 morbidity to date, is predominantly due to the continuing epidemiologic situations in Barbados and Trinidad and Tobago, as those countries accounted for 34.9 (391/914) and 61.6 percent (563/914) of the total regional notifications, respectively.

The weekly numbers of reported cases of dengue fever for 1998 were compared with historic weekly means (1990-1997) and a threshold value equivalent to 1.3 standard deviations above the historic mean. Reported 1998 morbidity exceeded the threshold value during each of the first seven weeks of the year. During epidemiologic weeks 8, 10, 11 and 12, current 1998 reporting levels, however, fell below the regional threshold values (Figure 1).

A review of the viral isolate data from CAREC’s laboratories reveals dengue activity in Guyana [DEN-1]; St. Vincent and the Grenadines [DEN-2]; Antigua and Barbuda [DEN-1]; and Suriname [DEN-1]. Additionally, dengue virus type 3 has continued to circulate in Belize, the only CAREC member country in which it has been identified to-date. While the type 2 virus appears to have been the only aetiologic agent circulating in Trinidad and Tobago during the first quarter of 1998, dengue serotypes 1, 2 and 4 were identified in Barbados during this period.

As indicated in previous Feedback Reports, dengue viruses are becoming hyperendemic in some of our member countries, a situation that increases the potential for the occurrence of dengue haemorrhagic fever and shock syndrome in these populations. Three cases of DHF were notified from Trinidad and Tobago during the epidemiologic period under review.

It is of interest and concern, that effective transmission of this vector-borne disease continued to be sustained at relatively high levels during the traditional dry season period of the year. Reports from Barbados suggest that Aedes aegypti house and Breteau indices have been approximately one percent during the quarter.

Evaluative as well as research studies are required to assess inter alia (a) the true magnitude of Aedes aegypti infestation; (b) whether the bionomics of the vector may be changing in this sub-region; (c) whether new, non-traditional breeding sites are becoming available to the vector; (d) whether insecticide resistance may be more widespread than is currently known; (e) whether human behaviour is enhancing the potential for mosquito breeding; (d) whether the high ambient temperatures and/or other weather-related El Nino effects experienced during this dry season may have impacted on breeding potential, etc.

Regardless of the findings of any research studies, effective control of the Aedes aegypti mosquito through concerted and joint action by national health authorities and local communities must be a priority if dengue fever is to be eliminated in the sub-region. Additionally, there is an urgent need to control this particular vector so as to prevent the potential emergence of urban yellow fever in the Caribbean.

Acute Respiratory Infections

Increased reporting of acute respiratory infections among children less than five years of age was observed during the first quarter of 1998 when 8,517 cases were recorded (Table 1). Although Guyana accounted for the greatest proportion of the overall notifications (65.9% or 5,615/8,517), Bermuda, the Turks and Caicos Islands, St. Lucia and the British Virgin Islands also recorded more cases of ARIs during this quarter than during the corresponding period of 1997. The increased notifications from Guyana are as a result of improvements in their surveillance procedures and process.

Measles

During the first quarter of 1998, 174 suspected cases of measles were notified through the Measles Elimination Surveillance System (MESS). While this figure is lower than the 284 cases recorded during the corresponding period of 1997 (Table 1; Figure 2), it was noted that roughly 65.0 percent of the overall cases were reported from Suriname. Increased dengue fever morbidity in Suriname would have contributed to the observed excess in the reported incidence of febrile rash illnesses.

Rubella

Although reported rubella activity during the first quarter of 1998 is significantly lower than that for the corresponding period of 1997 (Table 1; Figure 3), cases of congenital rubella syndrome continue to be notified.

Typhoid Fever

Of the 97 cases of typhoid fever reported from CAREC-member countries during this quarter, 93.8 percent (91/97) were notified from Guyana. These cases which have been described as clinically suspect, have not been laboratory confirmed by culture.

Viral Hepatitis A

Of the 156 cases of viral hepatitis A reported from our member countries during this quarter, 95.5 percent (149/156) were recorded in the Bahamas, where there has been sustained viral activity since the outbreak of July 1997.

A General Comment