Study Design : Time Series for the Larvitrap Index and Cohort Study for incidence of dengue.
Selection of the Study Area : V & G subdivision was selected as the study area since it had the highest report of dengue fever cases (60/1360 or 3%) in Tacloban City based on records of the Regional Epidemiology & Surveillance Unit (RESU), DOH 8 in 2002.
Sample size computation : Using the Epi-Info Program, the sample size for the study was computed as shown below: Population size : 2,835 households, Expected frequency : 25%, Worst acceptable : 35%, Confidence level : 95%, Sample size : 70 households.
Sampling of Households for Larvitrap Index : The stratified sampling technique was used in selecting the study households. Since households from, the 2 barangays were addressed by phase, (ex. Phase 1,2,3. etc.) each phase was considered a stratum. Then, representative number of households, consisting of 2.5% of the total number of households in each stratum, was purposely selected to spread out the sample. Since the two (2) barangays had 5 phases each, a total of 10 stratum samples have been identified. The household was then identified by the phase, block, lot and house number as well as the street and some markers where they were exactly located. Brgy. 109-A & Brgy. 109 had 48 and 35 households respectively, making a total of 83 households included in the study. These households were then assigned to be given the Larvitrap and referred to as the index "households".
Results : The Larvitrap Index of Aedes mosquito dengue vector was generally higher in outdoor location than indoor location throughout the year in the study area. In 8/12 (67%) months, the monthly average Larvitrap Index for outdoor was higher compared to indoor including the hot-dry months of February, March & April 2003. There was a positive relationship observed between the Larvitrap Index of Aedes mosquito dengue vector (indoor and outdoor location) and the rainfall pattern in Tacloban City. When rainfall was heavy in the months of June and October, 2003, the Larvitrap Indices were quite high in August and December 2003, respectively. There were two (2) climatic seasons in Tacloban City observed during the study period based on the amount of rainfall in a particular month. The pronounced dry season was noted from February to May 2003 and the pronounced wet season was from June to January 2004. The Outdoor Larvitrap Index in the dry season (32.0%) was the same as the wet season (32.0%). Both Aedes vectors of dengue breed inside and outside household premises. However, the preference of Aedes aegypti was more for indoor location as compared to Aedes albopictus which preferred to breed more in outdoor location.
Conclusion : The study provided a strong evidence that the Aedes mosquito dengue vector followed no seasonal pattern in a dengue-sensitive area such as V & G subdivision. Tacloban City since no population fluctuation has been observed both in dry and wet months of the year 2003. The Larvitrap Index of Aedes aegypti was steadily high as a result of the large population of Aedes mosquito contributed by the different breeding containers that were found in the surrounding of the subdivision.