Integrated vector management with additional pre-transmission season thermal fogging is associated with a reduction in dengue incidence in Makassar, Indonesia: Results of an 8-year observational study

Abstract

Dengue virus transmission is endemic in Makassar, Indonesia, with the majority of cases reported soon after the start of the annual rainy season. Before 2006, larval source reduction, larvaciding, and reactive routine, outdoor, insecticide fogging campaigns did not result in a reduction in seasonal dengue incidence. Beginning in 2006, village volunteers conducted comprehensive surveys for immature Aedes during the dry season, when vector populations were at their lowest. Based on this pre-season vector data, a single additional pre-emptive outdoor fogging with Malathion was conducted once annually before the rains began in villages with a pre-defined proportion of sampled houses positive for Aedes immatures. This additional procedure was associated with reduced temporal larval indices as well as an 83% reduction in reported cases during the transmission season over the 8-year period of implementation. Two cities adjacent to Makassar experienced substantial but smaller reductions in dengue incidence; while other cities further from the intervention area did not. This represents the first time an integrated intervention strategy has been coupled with substantially reduced dengue transmission in Indonesia.

Fig 1. Relationship between rainfall and cases of Dengue as reported by the Ministry of Health (MoH) of Makassar City.

(A) A slight lag seen in increased Dengue cases and the onset of rainfall during the transmission season every year before the intervention. (B) After implementation of the revised program of larval surveys followed by fogging in selected areas based on HI, an immediate and sustained decrease is seen in dengue cases for 8 years. Green boxes denote the period of larval surveys, while the blue boxes depict the period of the additional pre-emptive, dry-season fogging, Note that rainfall does not significantly change pre and post intervention.

Fig 2. A Box-plot demonstrating the differences in incidence in Makassar and the neighboring cities of Maros and Gowa, pre (2003–2006) and post (2007–2014) intervention.

There was a significant reduction in incidence in Makassar pre and post intervention (Mann Whitney U test, p = 0.007), a decrease in Maros (p = 0.042), and a non-significant decrease in Gowa (p = 0.497). Population level data (and hence incidence calculations) were only present from 2003 onwards.

Fig 3

A) Distance visualization of several cities been compared to Makassar on its dengue annual cases. The cities of Gowa and Maros that flank Makassar are depicted along with the location of the five largest cities outside Makassar. The inset depicts the location of South Sulawesi within Indonesia. Blue indicates cities with decreased reported dengue while orange indicates cities with increased dengue (Map Source: Hand drawn). B) Change in annual reported cases post intervention in South Sulawesi. Change in average annual reported dengue cases post intervention in the 23 major cities in South Sulawesi in order of distance away from Makassar. An * denotes cities on the map in (A). MKS = Makassar*, GW = Gowa*, MR = Maros*, TKL = Takalar*, PK = Pangkep*, JP = Jeneponto, BR = Barru, BT = Bantaeng, BLK = Bulukumba*, PR = Pare-Pare*, SP = Soppeng, PNR = Pinrang, SR = Sidrap, WJ = Wajo, SJ = Sinjai, ER = Enrekang, PM = Polmas, SL = Selayar, BN = Bone*, TT = Tana Toraja, LW = Luwu, LU = Luwu Utara.

Fig 4. Reduction of Aedes Larval Densities—House Indexes (HI), in Makassar from 2008 to 2014.

HI is indicated by color: Red = greater than 40%, Orange = 35% to 40%, Pink = 25% to 34% and white = 0% to 24%. (Map Source: ArcGIS 10.6).