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. 2015 Jun 24;10(6):e0131423.
doi: 10.1371/journal.pone.0131423. eCollection 2015.

Impacts of different grades of tropical cyclones on infectious diarrhea in Guangdong, 2005-2011

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Impacts of different grades of tropical cyclones on infectious diarrhea in Guangdong, 2005-2011

Ruihua Kang et al. PLoS One. .

Abstract

Objective: Guangdong province is one of the most vulnerable provinces to tropical cyclones in China. Most prior studies concentrated on the relationship between tropical cyclones and injuries and mortality. This study aimed to explore the impacts of different grades of tropical cyclones on infectious diarrhea incidence in Guangdong province, from 2005 to 2011.

Methods: Mann-Whitney U test was firstly used to examine if infectious diarrhea were sensitive to tropical cyclone. Then unidirectional 1:1 case-crossover design was performed to quantitatively evaluate the relationship between daily number of infectious diarrhea and tropical cyclone from 2005 to 2011 in Guangdong, China. Principal component analysis (PCA) was applied to eliminate multicollinearity. Multivariate logistic regression model was used to estimate the hazard ratios (HRs) and the 95% confidence intervals (CI).

Results: There were no significant relationships between tropical cyclone and bacillary dysentery, amebic dysentery, typhoid, and paratyphoid cases. Infectious diarrhea other than cholera, dysentery, typhoid and paratyphoid significantly increased after tropical cyclones. The strongest effect were shown on lag 1 day (HRs = 1.95, 95%CI = 1.22, 3.12) and no lagged effect was detected for tropical depression, tropical storm, severe tropical storm and typhoon, with the largest HRs (95%CI) of 2.16 (95%CI = 1.69, 2.76), 2.43 (95%CI = 1.65, 3.58) and 2.21 (95%CI = 1.65, 2.69), respectively. Among children below 5 years old, the impacts of all grades of tropical cyclones were strongest at lag 0 day. And HRs were 2.67 (95%CI = 1.10, 6.48), 2.49 (95%CI = 1.80, 3.44), 4.89 (95%CI = 2.37, 7.37) and 3.18 (95%CI = 2.10, 4.81), respectively.

Conclusion: All grades of tropical cyclones could increase risk of other infectious diarrhea. Severe tropical storm has the strongest influence on other infectious diarrhea. The impacts of tropical cyclones on children under 5 years old were higher than total population.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Study areas in Guangdong Province, China, from 2005 to 2011.
All reported infectious diarrhea cases in landfall cities from 2005 to 2011 were included in this study. In addition, we analyzed the impacts of tropical cyclones upon occurrence of infectious diarrhea among high risk population of "≤ 5 years" group.
Fig 2
Fig 2. Case and control periods defined in the case-crossover design.
In addition, principal component analysis (PCA) was used to eliminate the multicollinearity among meteorological factors. PCA was an effective method to reduce the dimensionality of a number of interrelated variables, while retaining the maximum variability in the data [22]. The standard of extracting principle components was that the eigenvector is larger than 1 and cumulative proportion reaches 70 percent to 85 percent. In this study, we confirmed 3 principle components. Then we tested the multicollinearity between tropical cyclone and three principle components and none was detected. Hence, tropical cyclone and three principle components were put into conditional logistic regression and hazard ratios (HRs) as well as 95% CI were calculated. Previous studies have reported a delayed onset of symptoms and subsequent hospitalization of diarrhea extreme precipitation [23]. Incubation periods of infectious diarrhea can range from one day (e.g., for Salmonella and Rotavirus) to up to one or two weeks (e.g., for Cryptosporidium, E.coli and Giardiasis) [20]. To account for the incubation periods, the 7-day lagged effects were considered in this study. All statistical analyses were performed using SAS 9.2 (SAS Institute Inc., USA).
Fig 3
Fig 3. HRs of tropical cyclones on the risk of other infectious diarrhea on different lagged days.
For total population, the impact of tropical depressions was largest at lag 1 day for other infectious diarrhea. The HR and 95% confidence interval was 1.95 (95%CI: 1.22, 3.12). The impacts of all tropical storms, severe tropical storms and typhoon were largest at lag 0 and HRs were 2.16 (95%CI = 1.69, 2.76), 2.43 (95%CI = 1.65, 3.58) and 2.21 (95%CI = 1.65, 2.69), respectively. For the "≤5 years" group, the influences of all tropical cyclones were largest at lag 0 for other infectious diarrhea. In another word, there were no delayed effects for tropical cyclones on other infectious diarrhea among "≤5 years" group. HRs were 2.67 (95%CI = 1.10, 6.48), 2.49 (95%CI = 1.80, 3.44), 4.89 (95%CI = 2.37, 7.37) and 3.18 (95%CI = 2.10, 4.81), respectively. Fig 3 also shows that the impacts of severe tropical storms were largest among all grades of tropical cyclones on other infectious diarrhea both for total population and "≤5 years" group.

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