Serological investigation to identify risk factors for post-flood infectious diseases: a longitudinal survey among people displaced by Typhoon Morakot in Taiwan

OBJECTIVES: After Typhoon Morakot struck Taiwan in 2009, thousands of Taiwanese citizens were displaced to shelters for several weeks. Others were placed in urban communities where they had family members. This study aimed to investigate serological status in both groups and identify risk factors associated with seroconversion of infectious diseases. DESIGN: A longitudinal survey. SETTING: All experimental and clinical investigations were performed in a tertiary teaching hospital. PARTICIPANTS: A total of 288 displaced persons (96 males and 192 females) were recruited and complete follow-up data through two rounds of sampling were collected. The average age was 58.42 years (range 31–87 years). INTERVENTIONS: First, serum specimens were collected between December 2009 and January 2010, 4–5 months after the typhoon. The second round of specimen collection was carried out after 6 months. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome measured was serological status of vaccine-preventable droplet-borne infectious diseases (ie, measles, mumps, rubella) and water-borne diseases (ie, amoebiasis and leptospirosis). The secondary outcome was identification of risk factors for seroconversion using univariate and multivariate analyses. RESULTS: Complete data were available for all 288 displaced persons (114 from the shelter group; 174 from the community group). Seroconversion of Entamoeba histolytica was observed in 128 (44.4%) participants, with a significantly higher rate in the shelter group than in the community group (56.1% vs 36.8%; p=0.001). There were 10 cases of rubella seroconversion. After adjusting for medical history, hypertension and hyperlipidaemia, shelter stay was associated with higher risk for seroconversion (OR=2.055, 95% CI 1.251 to 3.374; p=0.004). Amoebiasis was more evident in the shelter group, although the manifestations were mild. CONCLUSIONS: Our results suggested that (1) a clean water supply is essential postdisaster, especially in crowded shelters, and (2) vaccination programmes should be extended to populations at higher risk for post-disaster displacement or to those with weakened immune status.