Construction sites an important contributor to dengue transmission

Spillover transmission of dengue viruses from construction sites is highly likely to occur and is critical for the surrounding residential areas, according to a Singapore study.

“The role of construction sites as an important driver of dengue transmission cannot be underestimated,” the authors said. “[D]engue control measures of construction site-associated clusters should not be limited to the sites per se, but to stretch out to a ‘buffer-zone’ in the surrounding residential areas to minimize sustained virus transmission.”

The authors looked at dengue cases recorded during 2013–2016 in Singapore and clustered based on proximity and onset dates, evaluating the propensity of construction site-associated clusters to grow into major clusters (≥10 reported cases). A cluster was defined as ≥2 cases occurring within 150 m apart from and 14 days of each other.

Of the 6,568 clusters documented, only around 5 percent were attributed to construction sites (range, 2.9 percent in 2013 and 2016 to 4.8 percent in 2014). However, a high proportion of construction site-associated clusters comprised major clusters (range, 20 percent in 2016 to 66 percent in 2013). [BMC Infect Dis 2018;doi:10.1186/s12879-018-3311-6]

In each year, construction site-associated clusters were significantly more likely to expand into major clusters compared with nonconstruction site clusters (odds ratios, 17.4 in 2013, 9.24 in 2014, 3.35 in 2015 and 4.29 in 2016; p<0.01).

Construction sites harboured higher Aedes premise index and average larvae count per habitat than residential premises. Yet, the majority of cases in clusters that were identified with construction sites occurred in residents living in the immediate periphery.

Virus genotype data from three case studies of large construction site-associated dengue clusters (Bedok reservoir road, Choa Chu Kang and Tampines) revealed a transmission link between the construction sites and the surrounding residential areas.

“These observations implied that the expansion of clusters was not purely attributable to cases in construction sites, but also due to the external neighbouring environment being conducive for virus transmission,” the authors said.

“Because the workers move around in the neighbourhood and mosquitoes could migrate between the construction sites and the external periphery, it is difficult to cease new cases until the transmission is interrupted in both environments,” they added.

Locally, construction sites are penalized, including being prosecuted in court and stopping work orders, for having poor housekeeping or when mosquito breeding is detected. The National Environment Agency (NEA) has also implemented the Environmental Control Officers Scheme mandating companies to take up the responsibility of minimizing vector breeding at large construction sites and protecting the staff from acquiring vector-borne diseases.

“As many dengue endemic countries in Asia and South/Central America have emerging economies and are undergoing rapid infrastructure upgrading, our findings have important implications for the policy planning and control of dengue in an era of rapid urbanization,” the authors said.