Abstract:

Objective To analyze the epidemiological characteristics and measures to manage dengue fever outbreaks in two construction sites in Shenzhen area, and summarize the experience in prevention and control of the two outbreaks. Methods Case finding was carried out in the surrounding areas and medical institutions of A construction site in Nanshan District and B construction site in Bao’an District where the epidemic occurred, and case exposure and epidemiological history, and clinical manifestations were investigated. Colloidal gold immunochromatography assay was used to detect the antibodies and antigens, and RT-PCR was used for nucleic acid detection and typing. Viral tracing was performed through next-generation sequencing. Mosquito vector density was measured using Breteau index (BI) and mosquito ovitrap index (MOI). Results The two outbreaks, occurring between September and November, involved 94 and 86 cases and lasted for 84 and 45 days, respectively. The cases were predominated by males (n=144; 80.00%) and population aged 30-59 years (n=143; 79.44%). Occupational distribution was primarily associated with workers (n=130; 72.22%). All cases were clinically classified as mild dengue fever. A total of 31 cases (32.98%) and 23 cases (26.74%) were respectively detected more than 5 days after symptom onset. Epidemiological investigations revealed that neither of the index cases in the two outbreaks had a travel history outside Shenzhen within 14 days prior to symptom onset. A presymptomatic case from Site A had resided in the worker’s dormitory at Site B 13 days prior to the onset of the outbreak at Site B. In the early stage of the two waves of the epidemic, the viruses infecting 24 cases were all dengue virus serotype Ⅰ, genotype Ⅰ, showing a homology of 99.90%. Finally, 180 cases were identified in 1 509 individuals screened. Targeted mosquito elimination and breeding site cleanup were conducted every 3 days at core epidemic foci in both worksites. The average daily BI and MOI both dropped to safe levels (BI ≤ 5 and MOI ≤ 5) on October 20th. The epidemic was declared over 25 days after the last case was reported, when no new cases emerged and the BI and MOI at both construction sites dropped below 5. Conclusion Both outbreaks were endemics spread across construction sites through asymptomatic infected migrant workers. The findings suggest that prevention and control of dengue fever at the construction site is involved in such problems as high mobility of personnel, weak awareness of seeking medical treatment, high density of mosquito vectors and difficulty in epidemic control, for which we recommend that it is necessary to implement various prevention and control measures, including case detection, mosquito vector control and worker management.

Key words: Dengue fever, Outbreak, Epidemiological investigation, Emergency response, Construction site