Seasonal variation among tuberculosis suspects in four countries

Monthly proportion of suspects and cases among total suspects and cases respectively (●cases ○suspects)

Brief description: From the monthly proportion of suspects and cases among total suspects and cases, seasonal variations are most marked in Mongolia which, among the four countries, also has the most pronounced seasonal variation in ambient temperature.

Proportion of cases among suspects by month (UCL: upper control limit; LCL: lower control limit)

Brief description: Statistical process control charts were used to summarize variation and uncertainty in the monthly proportions of cases among suspects in the four countries. In Mongolia, these proportions show a definite excess proportion of cases among suspects in June and July, followed by a considerable decline to below average proportions from August through December. Lower than expected proportions were found in March in Moldova and Zimbabwe and in April in Uganda, while a higher than expected prevalence was recorded in September in Zimbabwe.

Proportion of males among suspects and cases by month (○suspects ■cases)

Brief description: In three countries, there were more males than females among suspects and cases. In all four countries, males were more likely to be cases than suspects, but the male-to-female case-to-suspect ratio was most pronounced in Moldova.

Mean age and 95% confidence interval among female suspects and cases by month (○suspects ●cases)

Brief description: Female suspects were consistently older than female cases in all four countries. In Moldova, female suspects were aged on average about 45 to 50 years, with little change throughout the year. In contrast, the mean age among female cases changed importantly over the course of a year, case patients tending to be youngest in the early part of the year and oldest in the second half.

Mean age and 95% confidence interval among male suspects and cases by month (□suspects ■cases)

Brief description: Among males, suspects were almost consistently older than cases, most consistently in Moldova. No clear seasonal pattern emerged in any of the four countries, neither among cases nor among suspects.