Abstract
BackgroundThere is paucity of data on seasonal variation in pulmonary tuberculosis (TB) in developing countries contrary to recognized seasonality in the TB notification in western societies. This study examined the seasonal pattern in TB diagnosis among migrant workers from developing countries entering Kuwait.MethodsMonthly aggregates of TB diagnosis results for consecutive migrants tested between January I, 1997 and December 31, 2006 were analyzed. We assessed the amplitude (α) of the sinusoidal oscillation and the time at which maximum (θ°) TB cases were detected using Edwards' test. The adequacy of the hypothesized sinusoidal curve was assessed by χ2 goodness-of-fit test.ResultsDuring the 10 year study period, the proportion (per 100,000) of pulmonary TB cases among the migrants was 198 (4608/2328582), (95% confidence interval: 192 – 204). The adjusted mean monthly number of pulmonary TB cases was 384. Based on the observed seasonal pattern in the data, the maximum number of TB cases was expected during the last week of April (θ° = 112°; P < 0.001). The amplitude (± se) (α = 0.204 ± 0.04) of simple harmonic curve showed 20.4% difference from the mean to maximum TB cases. The peak to low ratio of adjusted number of TB cases was 1.51 (95% CI: 1.39 – 1.65). The χ2 goodness-of-test revealed that there was no significant (P > 0.1) departure of observed frequencies from the fitted simple harmonic curve. Seasonal component explained 55% of the total variation in the proportions of TB cases (100,000) among the migrants.ConclusionThis regularity of peak seasonality in TB case detection may prove useful to institute measures that warrant a better attendance of migrants. Public health authorities may consider re-allocation of resources in the period of peak seasonality to minimize the risk of Mycobacterium tuberculosis infection to close contacts in this and comparable settings in the region having similar influx of immigrants from high TB burden countries. Epidemiological surveillance for the TB risk in the migrants in subsequent years and required chemotherapy of detected cases may contribute in global efforts to control this public health menace.
Highlights
There is paucity of data on seasonal variation in pulmonary tuberculosis (TB) in developing countries contrary to recognized seasonality in the TB notification in western societies
Migrant worker was classified as a TB case if sputum smear and/or bacterial culture was positive for acid fast bacilli (AFB) [21]
The Edwards' model revealed that based on the observed seasonal pattern in the data, the significant peak in number of TB cases was expected during the last week of April (θ° = 112°; P < 0.001)
Summary
There is paucity of data on seasonal variation in pulmonary tuberculosis (TB) in developing countries contrary to recognized seasonality in the TB notification in western societies. From 1989 to 1999, there was a steady increase in the TB incidence among both nationals and non-nationals suggestive of Mycobacterium tuberculosis transmission from non-nationals to nationals since a large proportion of migrants from South Asian and South-East Asian countries live and work in Kuwaiti homes as domestic workers [8]. This reversal of the observed TB trend in Kuwait may be explained in part by the disruption of TB control program following first Gulf War in 1990 [8], and by the concomitant increase in the proportion of migrants from high TB burden countries [9]. The epidemiologic importance of migration from high TB incidence to low TB incidence countries has been recognized for several years; the main countermeasure has been the implementation of screening programs for immigrants at the time of arrival, and providing required chemotherapy [10,11]
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