Malaria, Oromia regional state, Ethiopia, 2001-2006

To the Editor: In Ethiopia, malaria is unstable and commonly occurs as intraannual and interannual epidemics. Transmission is associated with altitude, temperature, and rainfall, generally peaking twice a year, after the 2 rainy seasons (March–May and July–September) (1). Cases are caused by Plasmodium falciparum and P. vivax. Anopheles arabiensis mosquitoes are the main vector for both species. Although malaria is the most common communicable disease in Ethiopia (2), few longitudinal case data has been published (3). We report a retrospective analysis of outpatient data for July 2001–June 2006 obtained from all secondary and tertiary government-run health facilities (152 health centers and 25 hospitals) in Oromia Regional State. Oromia has 17 administrative zones and 297 districts. Data were reported monthly on paper forms by health facility staff at district level to the Oromia Regional Health Bureau Zonal Health Offices, which aggregated zonal data before forwarding them to the Oromia Regional Health Bureau Malaria Control Department. Data obtained included number of outpatient cases (i.e., patients attending the health facility grouped by age 5 years); number of clinical malaria cases (i.e., patients with fever grouped by age and sex); number of clinical cases confirmed by microscopy; and number of cases caused by P. falciparum and P. vivax. If no outpatient data were reported, the case number was changed from zero to missing. The data were entered into Microsoft Excel (Microsoft, Redmond, WA, USA) and analyzed by using Stata version 9.0 (StataCorp LP, College Station, TX, USA). During 2001–2006, a total of 8,786,088 outpatient consultations were reported. A total of 905,467 and 562,996 clinical and confirmed malaria cases, respectively, were reported. Patients were predominantly seen at health centers rather than at hospitals, with 80.2% clinical and 72.2% confirmed malaria cases seen at health centers. Clinical malaria accounted for 10.3% of outpatient consultations in all facilities. However, this percentage varied between years (6.1%–16.0%) and zones (1.3%–21.9%) (Technical Appendix Figure 1). Of clinical malaria cases, 16.5% were in children 75% of the clinical cases seen at health facilities during 2001–2006. Malaria incidence varied between years: clinical and confirmed cases increased in 2003, the last epidemic year recorded in Oromia (5), before decreasing to 2001 levels in 2004 (Technical Appendix Figure 1). The P. falciparum to P. vixax ratio changed geographically and temporally (Technical Appendix Figure 1), and increases in the proportion of P. falciparum cases coincided with the peak malaria transmission season. In the epidemic year of 2003, the proportion of P. falciparum cases was larger than in other years, and children