Intensity of rainfall and severity of melioidosis, Australia - Research

Emerging Infectious Diseases, Dec, 2003 by Bart J. Currie, Susan P. Jacups

Results

The Figure shows the close association between total monthly rainfall, as recorded at Darwin Airport, and the number of cases of melioidosis in the Top End for each month during the 12 years. The correlation between monthly cases of melioidosis and rainfall at Darwin Airport in the preceding calendar month (r = 0.617; p < 0.0001) was slightly tighter than the correlation with rainfall in the concurrent month (r = 0.574).

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Table 1 shows the median 14-day rainfall correlation with various risk factors, clinical signs and symptoms, and outcomes. The correlation with median 14-day rainfall was significantly higher for patients with pneumonia, those with bacteremia and septic shock, and those who died. For those patients with pneumonia, correlation with median 14-day rainfall was significantly higher if they were bacteremic. Patients with diabetes, alcohol excess, and chronic renal disease were all associated with significantly higher median 14-day rainfall; correlation with 14-day rainfall did not significantly differ for age, sex, ethnicity, chronic lung disease, and smoking (data not shown).

Table 2 shows that, on univariate analysis, 14-day rainfall [greater than or equal to] 125 mm correlated significantly with primary symptoms of pneumonia, bacteremia, and septic shock, and with death. Table 3 shows independent predictors of clinical signs and symptoms and outcome when multivariate analysis with 14-day rainfall as a categorical variable was used. When 14-day rainfall was used as a continuous variable, it was an independent risk factor for admission with primary symptoms and signs of pneumonia (p = 0.023), bacteremic pneumonia (p = 0.001), septic shock (p = 0.005), and of death (p < 0.0001). Notably, while absence of any risk factors was a predictor of primary signs and symptoms other than pneumonia and of less severe disease, neither diabetes, alcohol excess, nor chronic renal disease was an independent predictor of signs and symptoms, disease severity, or death.

Discussion

Our data confirm our observations that patients admitted with melioidosis 1-2 weeks after heavy monsoonal rainfall are more ill and more likely to die. Median rainfall in the 14 days before admission was highest (211 mm) for those who died with melioidosis. For those admitted with bacteremic pneumonia, prior 14-day median rainfall was 188 mm, compared with 89 mm in patients who were nonbacteremic and did not have pneumonia. Multivariate analysis showed that rainfall in the 14 days before admission was an independent predictor of septic shock and death. Patients were 2.5 times more likely to die from melioidosis if the rainfall in the 14 days before admission was [greater than or equal to] 125 mm. Overall, 68% of deaths occurred in this high rainfall group. Furthermore, prior heavy rainfall was an independent predictor of admission with pneumonia rather than with no pneumonia. Patients were almost twice as likely to have bacteremic pneumonia if the rainfall in the 14 days before admission was [greater than or equal to] 125 mm.