The burden of cholera in Uganda

Abstract

Introduction: In 2010, the World Health Organization released a new cholera vaccine position paper, which recommended the use of cholera vaccines in high-risk endemic areas. However, there is a paucity of data on the burden of cholera in endemic countries. This article reviewed available cholera surveillance data from Uganda and assessed the sufficiency of these data to inform country-specific strategies for cholera vaccination.

Methods: The Uganda Ministry of Health conducts cholera surveillance to guide cholera outbreak control activities. This includes reporting the number of cases based on a standardized clinical definition plus systematic laboratory testing of stool samples from suspected cases at the outset and conclusion of outbreaks. This retrospective study analyzes available data by district and by age to estimate incidence rates. Since surveillance activities focus on more severe hospitalized cases and deaths, a sensitivity analysis was conducted to estimate the number of non-severe cases and unrecognized deaths that may not have been captured.

Results: Cholera affected all ages, but the geographic distribution of the disease was very heterogeneous in Uganda. We estimated that an average of about 11,000 cholera cases occurred in Uganda each year, which led to approximately 61-182 deaths. The majority of these cases (81%) occurred in a relatively small number of districts comprising just 24% of Uganda's total population. These districts included rural areas bordering the Democratic Republic of Congo, South Sudan, and Kenya as well as the slums of Kampala city. When outbreaks occurred, the average duration was about 15 weeks with a range of 4-44 weeks.

Discussion: There is a clear subdivision between high-risk and low-risk districts in Uganda. Vaccination efforts should be focused on the high-risk population. However, enhanced or sentinel surveillance activities should be undertaken to better quantify the endemic disease burden and high-risk populations prior to introducing the vaccine.

Figure 1. Annual number of cholera cases and deaths reported in Uganda 1997–2010.

There was a major outbreak in 1998 and a fluctuating, but persistent burden of cholera in the years since the outbreak.

Figure 2. Districts with reported cholera cases from 2005 to 2010 (endemic and non-endemic districts).

Some districts may be considered endemic for cholera based on a history of cholera incidence during three of the five years from 2005–2010. Other districts have demonstrated cholera on a less consistent basis, while a few districts did not report any cases between 2005–2010.

Figure 3. Age breakdown of cholera cases from non-random sample of cholera outbreaks, 2002–2010.

The percentage distribution of cholera cases in Uganda is similar to the overall age distribution of the population.

Figure 4. Distribution of deaths by age group and average case fatality rate by age group.

The age distribution of cholera deaths varies slightly from age distribution of cases because the case fatality rates are higher infants and the elderly relative to other age groups.

Figure 5. Map of reported cholera incidence by district, hospitalized cases, 2005–10.

The estimated incidence by district varies considerably in Uganda with a distinct pattern of low-incidence versus high incidence districts.

Figure 6. Epidemic curves of cholera outbreaks in Uganda, 2002–2010.

The epidemic curves from a convenience sample of fifteen outbreaks shows both large and small outbreak have occurred during the period 2002–2010. There is considerable variation in the duration of outbreaks with longer outbreaks in districts with higher average annual incidence rates.