Communicable Diseases Feedback Report

Reporting Period: Epidemiologic Weeks 45-53 of 1997

A Review of Selected Communicable Diseases

DENGUE FEVER

During the period under review (epidemiologic weeks 45-53 of 1997), 2,233 cases of dengue fever were officially notified to CAREC's Epidemiology Division, representing a 2.8-fold increase in reported morbidity over that for the corresponding period in 1996. Barbados and Trinidad and Tobago were the sole contributors to this marked increase in dengue fever virus activity as they accounted for 1,470 (65.8%) and 706 (31.6%) of the total cases recorded, respectively. The pattern of the epidemic curves for both of these CAREC member countries (CMCs) was similar over the last quarter, differing only in magnitude (Figure 1). Haemorrhagic cases were also documented in both of these CMCs.

In 1996, 5,137 cases of dengue fever were notified to CAREC for a subregional incidence rate of 80.5 cases per 100,000 population. In that year, significant virus activity was noted in Trinidad and Tobago, from which 77.5 percent of the total notifications ( 3,983/5,137) were derived. In 1997, however, 3,892 cases of this disease were reported for a subregional incidence rate of 59.4 cases per 100,000 population (Figure 2; Table 1). Although the overall 1997 morbidity is reportedly lower than that for 1996, it is interesting to note that notifications of dengue fever were significantly increased during the 12th four-week period of 1997.

In order to compare current dengue fever activity with historical data, the traditional reporting weeks were divided into 13 four-weekly periods. The means for each consecutive four-week period over the years 1990 through 1996 (excluding 1995) were calculated and a threshold level established equivalent to plus 1.30 standard deviations. During 1997, the four weekly means of reported cases for all except the 12th period fell below the estimated threshold levels for the sub-region (Figure 3).

During 1997, dengue virus types 1 and 2 were the predominant aetiologic agents circulating in most of our member countries, although virus type 4 was recovered on one occasion and type 3 virus was identified for the first time in Belize (Table 2). The intense type 2 transmission that has observed within a relatively short period of time following type 1 activity has increased the potential for the occurrence of DHF in some of our populations.

MEASLES

During the period under review 98 cases of suspected measles were referred to the Expanded Programme on Immunisation through the Measles Elimination Surveillance System (MESS). During 1997, a cumulative total of 1,004 suspected cases were notified from 16 countries of the English-speaking Caribbean and Suriname as compared with 471 cases in 1996 (Figure 4). Only two of these cases were, however, confirmed as measles, one having been imported into Trinidad and Tobago from Italy and the other having originated in the Bahamas. It should be noted that in 1997, 28.8 and 2.1 percent of the suspected measles referrals were confirmed as rubella and dengue fever, respectively.

RUBELLA

Seventy-one cases of rubella were notified during this reporting period as compared with 121 cases during the corresponding period of 1996. Overall, during 1997, 565 cases were reported for a subregional incidence rate of 8.6 cases per 100,000 population (Figure 5). Nearly half of all the notified cases, 44.7 percent, were reported from Trinidad and Tobago. It should be noted that these rubella notifications to CAREC's Epidemiology Division as part of the general communicable diseases reporting system may possibly not include those 283 cases which were laboratory confirmed through the rash-fever surveillance system of the EPI/MESS.

Over 20 cases of congenital rubella syndrome were documented in the subregion during 1997, but these will be reviewed in detail in a separate document.

GASTROENTERITIS

During 1997, notifications of gastroenteritis both among the under and over five populations were significantly increased in Antigua, the Cayman Islands, Jamaica and St. Christopher/Nevis. During 1997, 4,738 cases of gastroenteritis were reported in total from Antigua, where an extensive outbreak due to rotavirus infection had occurred during the early months of the year.

VIRAL HEPATITIS A

Reported morbidity due to hepatitis A viral infection in 1997 was nearly double that recorded during 1996. While the Bahamas was most affected, reporting 85.0 percent of the total cases, CAREC's laboratories were also able to document increased viral transmission in Suriname and the Turks and Caicos Islands.

Dr. M.J. Lewis and Team
CAREC's Epidemiology Division