RESUMEN
Objective To study the association between temperature and daily mortality from June 1, 2006 to December 31, 2009 in Guangzhou. Methods Time series approach was used to estimate the impact of temperature on the rates of total and cause-specific daily mortality. We fitted generalized additive Poisson regression using non-parametric smooth functions to control for the long-term time trend, day of week, air pollution and other weather variables. Results A slight sloping U-like relationship between the total mortality and temperature was found, with an optimum average temperature (temperature with lowest mortality risk) value of 19.7 ℃ in Guangzhou. For temperature above the optimum value, the relative risk of total mortality increased by 3.0% (RR=1.030,95%CI: 1.011-1.050) for each increase of degree in Celsius. For average temperature below the optimum value, the relative risk of total mortality and diseases of circulatory system had a 3.3%(RR=0.967,95%CI: 0.936-0.997 ) decrease and a 3.6% ( RR= 0.964,95%CI:0.935-0.994 ) increase,for each degree of Celsius increase, respectively. Conclusion Our findings showed that the temperature had an impact on the daily mortality in Guangzhou. Countermeasures needed to be taken to reduce the temperature related mortality.
RESUMEN
Objective To explore the impact and regularity of snail population after changing of water level and to develop effective control and prediction programs. Methods A typical snail habitat closed to Changjiang county in Yueyang city, Hunan province was selected as the survey field.Data on water level and the changing trend of snail population during 2001-2009 including the average water level, maximum and minimum water levels, snail and infected snail densities,proportion of sampling frames with living and infected snails etc. were collected. The distribution of water level and snail indexes were described and a general additive model(GAM)for the relationships between these indexes were also fitted. Results Impacts of the average water level and the watered-out days in current year in the surveyed field on the snail density were statistically significant(P＜0.01), showing a quadratic curve association. The snail density remained at the lowest level when the average water level was at 25.0 m and the surveyed field watered-out days was 120. The average water level in current year and the field watered-out days in the past year showed statistically significant impacts on the infected snail density(P＜0.001), the proportion of sampling frames with infected snails(P＜0.05)and living snails(P value neared 0.05), presented a quadratic curve, a cubic curve or even a more complicated piecewise curve association. Both the infected snail density and the proportion of sampling frames with infected snails remained at the lowest level when the average water level was at 25.0 m and the watered-out days in the past year was 110, while the proportion of sampling frames with living snails kept the lowest level when the average water level was at 25.0 m and the watered-out days in the past year was 160. Conclusion The water level and the field watered-out days affected the development of snail population directly. The changing water level had an impact on snail population change, which mainly presented as nonlinear smooth function relation. Impact of the field watered out days on the infected snail density and the proportion of sampling frames with living snails and infected snails showed a hysteresis effect. The snail density was predicted to be retaining a high level when the water level was 24.0 m and the field watered-out days was 3 months. It had obvious advantages to fit the relationship of the changing water level and the snail indexes with a GAM which could get closer to the reality as well as easier to find and explain the potential associations and regulations.
RESUMEN
Objective To explore the relationships between micro-ecological environmental factors and the density of Snails so as to provide information for the elimination of Snails and control of Schistosomiasis disease,under ecological methods.Methods A bottomland close to Junshan Park in Yueyang city,Hunan province was selected as the field for survey during 10,2007-10,2008,and a systematic sampling method was applied to determine the specific sites of Snail investigation.All the Snails in each frames were collected and the soil surface temperature and vegetation coverage in several frames were measured.30 g soil sample in each selected frames were also collected simultaneously.The number of live Snails in each frame was counted by dissection,and soil measured pH value and soil moisture were tested in the laboratory.The distribution of Snails and microecological environmental factors,fitted general additive model for the relationship of these factors and the Snail density were described.Results 104 frames were surveyed,with pH value as between 4.70-7.92,vegetation coverage as in 1% to 96%,soil surface temperature as in 14.5-32.7℃,the soil moisture as in 0.07-2.00.Under General additive model,data showed that there was no significant difference for vegetation coverage.However,other factors were all significantly different(P＜0.001).It was found that a nonlinear relationship was existing between these factors and the Snail density.Conclusion Smoothing function relationship was noticed between the Snail density and micro-ecological environmental factors.It's suggested to fit general additive model to study the relationship between the distribution of Snails and its influencing factors,so as to adopt appropriate measures to change the related ecology to control the diffusion and reproduction of Snails.