Burden and Historical Trend of Buruli Ulcer Prevalence in Selected Communities along the Offin River of Ghana

Abstract

Buruli ulcer (BU) is a neglected tropical skin disease caused by Mycobacterium ulcerans with more than two thirds of the global cases reported in West Africa. A nationwide active BU case search conducted in 1999 identified two health districts along the Offin River as two of the three most endemic districts in Ghana. Based on recent anecdotal accounts that transmission is unstable along the Offin River, we conducted from March to June 2013 an exhaustive household survey and active case search in 13 selected communities within a five-kilometer radius along the Offin River. The overall prevalence of BU was 2.3% among the surveyed population of 20,390 inhabitants and 477 of the total 480 cases detected (99.4%) were historical (healed) cases. By estimating the year of occurrence for each case per community and taking into account available passive surveillance records of health facilities and the District Health Directorate, we observed a general trend of continuous emergence of cases in communities located midstream the Offin River whereas downstream communities showed more sporadic patterns. We monitored the incidence of cases after the survey and recorded a cumulative incidence rate of 0.04% for the 13 communities over a 17-month active surveillance period from August 2013 to December 2014. Our data reveal an overall decline in BU incidence along the Offin River similar to the general decline in BU incidence in recent years reported by the World Health Organization for West Africa.

Fig 1. Study area.

Map of Ghana showing major river systems. Our study area comprised part of the Offin river basin, shown here with a red rectangle. The Pra River is indicated by the dotted line.

Fig 2. Land cover and use in selected communities along the Offin river.

Upstream communities (A) Bedomase and (B) Krakrom, mid-stream community (C) Ntobroso and downstream community (D) Pokukrom.

Fig 3. Elevation and distribution of Buruli ulcer burden along the Offin River.

(A) A map showing communities located within the 5 km buffer along the Offin river. The 10 red colored study communities were randomly selected, the three yellow colored communities were added to the study based on recommendations by local health staff. (B) Spatial distribution of Buruli ulcer prevalence along the Offin river. (C) Spatial altitudes variation (indicated in feet) along the Offin river. The Mampong highland area is indicated by the yellow star. Community codes; Bedomase (A), Krakrom (B), Kapro (C), Akomfore (D), Ntobroso (E), Achiase (F), Keniago (G), Tontonkrom (H), Dominase (I), Nkotumso (J) Wromanso (K), Mfantseman (L) and Pokukrom (M).

Fig 4. Population age distribution and age adjusted prevalence of BU in the surveyed population.

(A) Age distribution of the surveyed population (n = 20,390 inhabitants) of the 13 selected study communities in the Offin river basin. (B) Age distribution of BU cases based on the age of the 480 identified cases at onset of the disease adjusted for age (per 1,000 inhabitants) using the age structure of the general surveyed population.

Fig 5. Estimated annual case trend for communities located mid-stream of the Offin river.

Trends were reconstructed using data from active survey (ACS) and passive surveillance data (PCS) available at the local and district health facilities. The red star represents unavailable passive surveillance data for a particular year. Community codes: D (Akomfore), E (Ntobroso), F(Achiase), G (Keniago), H (Tontonkrom). No case was detected in Bedomase (A) and index cases were detected in Krakrom (B) and Kapro (C).

Fig 6. Estimated annual case trend for communities located down-stream of the Offin river.

Trends were reconstructed using data from active survey (ACS) and passive surveillance data (PCS) available at the local and district health facilities. The red star represents unavailable passive surveillance data for a particular year. Community codes: I (Dominase), J (Nkotumso), K (Wromanso), L (Mfantseman), M (Pokukrom).

Fig 7. Monthly active surveillance of BU in the Achiase community.

Graph shows data obtained from Achiase by monthly household visits. Black bars represent percentage of households covered by the volunteer, grey bars represent the number of suspected cases and white bars represent the number of laboratory confirmed cases.