St. Mary’s Hospital, Lacor (http://www.lhospital.org ), is a Catholic mission hospital established in 1959 in Gulu in northern Uganda about 350 km from Kampala, Uganda’s capital. With ~500 beds (108 for children) and treating ~280,000 patients annually, it is the 3rd largest hospital in the country, offering general and specialized services to people living within ~100 mile radius. BL treatment is given at no cost to patients. A BL registry was established in 1992 to keep track of patients. Cases are diagnosed clinically and confirmed using cytology or histology by a senior pathologist at Makerere University Medical School in Kampala. Data were available on age, sex, tribe, address (district, sub-county, parish or village), date of admission, duration of symptoms, diagnosis and tumor location. Analysis was restricted to cases from 10 neighboring districts (locator map in Figure 1 ) treated from 1997 through 2006, years for which registry data were considered reasonably complete. Northern Uganda lies in savannah woodland between 2000-4000 feet above sea level and receives ~1000-1500 mm of rainfall in two seasons from March through June (heavy rains) and from September through November (light rains). Average temperature is 60-80° F and humidity is ~30%, and malaria transmission is holoendemic year-around. Historically, BL incidence was higher in northern than in southern Uganda (~3-4-fold). The average population density is low compared to the country average (65 vs. 124/ km2) and people live in grass-thatched houses on small subsistence farms. The population is mostly Nilotic, with 80% belonging to the Luo tribes of Acholi or Langi. About 60% of the population live within 5 km of a health center or hospital and have relatively easy access to transport. We assumed that BL cases from this region would be referred to Lacor Hospital because it is the only hospital in the region with facilities to both diagnose and treat BL.
We calculated BL incidence in children (ages 0-14 years) using annual (mid-year) age- and sex-specific-population projections obtained from the Uganda Bureau of Statistics. The population data included district-level population counts from the 1991 and 2002 censuses and the mid-year population estimates for the inter-censual years from 1992-2001 and extrapolations from 2003-2006, and age-, sex-, parish-level (Parish is the smallest administrative unit in a district for which population counts are obtained during census) population census data from the 2002 census. To impute county-level populations by year, we used the Parish census data for 2002 in combination with the district data for each year, assuming that the age-specific distributions in a given county remained the same across the study period. Overall, district-, county-, age-, sex-, calendar-period-specific BL incidence and standardized incidence ratios with 95% confidence intervals (CI) by county were calculated. The expected numbers of cases were calculated by applying age-, race-, sex-, calendar year-, and registry-specific incidence rates from the combined population to the person-time distribution in the district or county. We assumed that incidence was determined by Poisson distribution. District and county incidence were also age-standardized to the world standard population of Segi (1960) by the direct method. Odds ratios of association and 95% confidence intervals (95% CI) between categorical variables were determined using chi-square tables, while differences in the means of continuous variables were determined using the unpaired t-test. Two-sided p-value <0.05 was considered statistically significant.
We calculated BL incidence in children (ages 0-14 years) using annual (mid-year) age- and sex-specific-population projections obtained from the Uganda Bureau of Statistics. The population data included district-level population counts from the 1991 and 2002 censuses and the mid-year population estimates for the inter-censual years from 1992-2001 and extrapolations from 2003-2006, and age-, sex-, parish-level (Parish is the smallest administrative unit in a district for which population counts are obtained during census) population census data from the 2002 census. To impute county-level populations by year, we used the Parish census data for 2002 in combination with the district data for each year, assuming that the age-specific distributions in a given county remained the same across the study period. Overall, district-, county-, age-, sex-, calendar-period-specific BL incidence and standardized incidence ratios with 95% confidence intervals (CI) by county were calculated. The expected numbers of cases were calculated by applying age-, race-, sex-, calendar year-, and registry-specific incidence rates from the combined population to the person-time distribution in the district or county. We assumed that incidence was determined by Poisson distribution. District and county incidence were also age-standardized to the world standard population of Segi (1960) by the direct method. Odds ratios of association and 95% confidence intervals (95% CI) between categorical variables were determined using chi-square tables, while differences in the means of continuous variables were determined using the unpaired t-test. Two-sided p-value <0.05 was considered statistically significant.
