Use of Routine Health Information System Data to Evaluate Impact of Malaria Control Interventions in Zanzibar, Tanzania from 2000 to 2015

Abstract

Background: Impact evaluations allow countries to assess public health gains achieved through malaria investments. This study uses routine health management information system (HMIS) data from Zanzibar to describe changes in confirmed malaria incidence and impact of case management and vector control interventions during 2000-2015.

Methods: HMIS data from 129 (82%) public outpatient facilities were analyzed using interrupted time series models to estimate the impact of artemisinin-based combination therapy (ACT), indoor residual spray, and long-lasting insecticidal nets. Evaluation periods were defined as pre-intervention (January 2000 to August 2003), ACT-only (September 2003 to December 2005) and ACT plus vector control (2006-2015).

Findings: After accounting for climate, seasonality, diagnostic testing rates, and outpatient attendance, average monthly incidence of confirmed malaria showed no trend over the pre-intervention period 2000-2003 (incidence rate ratio (IRR) 0.998, 95% CI 0.995-1.000). During the ACT-only period (2003-2005), the average monthly malaria incidence rate declined compared to the pre-intervention period, showing an overall declining trend during the ACT-only period (IRR 0.984, 95% CI 0.978-0.990). There was no intercept change at the start of the ACT-only period (IRR 1.081, 95% CI 0.968-1.208), but a drop in intercept was identified at the start of the ACT plus vector control period (IRR 0.683, 95% CI 0.597-0.780). During the ACT plus vector control period (2006-2015), the rate of decline in average monthly malaria incidence slowed compared to the ACT-only period, but the incidence rate continued to show an overall slight declining trend during 2006-2015 (IRR 0.993, 95% CI 0.992-0.994).

Interpretation: This study presents a rigorous approach to the use of HMIS data in evaluating the impact of malaria control interventions. Evidence is presented for a rapid decline in malaria incidence during the period of ACT roll out compared to pre-intervention, with a rapid drop in malaria incidence following introduction of vector control and a slower declining incidence trend thereafter.

Keywords: Health management information systems (HMIS); Impact evaluation; Malaria; Zanzibar.

Fig. 1

Map of Pemba and Unguja Islands, Zanzibar, with district boundaries (left). Locater map with Tanzania Mainland and Zanzibar shaded (right).

Fig. 2

Total monthly all-cause outpatient department (OPD) attendance, total tested for malaria using microscopy or rapid diagnostic test, and total of confirmed malaria cases by island (Unguja and Pemba), plotted on a log scale.

Fig. 3

Monthly incidence of confirmed malaria per 100,000 population reported to HMIS, displayed by district. Wete and North B districts, although excluded from the ITS model, are included for the period in which parasitological diagnosis was available at facilities (from January 2006 in Wete, from January 2007 in North B). Vertical reference lines indicate the timing of interventions: introduction of ACTs as first line malaria treatment in September 2003 (leftmost vertical line), and large-scale introduction of IRS and LLINs in January 2006 (rightmost vertical line).

Fig. 4

District-level plots of the observed confirmed malaria incidence per month (gray line), predictions of incidence from the final interrupted time series model (blue line) and 95% confidence interval of the model prediction (pale blue shading). Vertical reference lines indicate the timing of interventions: introduction of ACTs as first line malaria treatment in September 2003 (leftmost vertical dotted line), and large-scale introduction of IRS and LLINs in January 2006 (rightmost vertical dotted line).

Fig. 5

Zanzibar-level plots of the observed confirmed malaria incidence per month (gray line), predictions of incidence from the final interrupted time series model (blue line) and 95% confidence interval of the model prediction (pale blue shading). Vertical reference lines indicate the timing of interventions: introduction of ACTs as first line malaria treatment in September 2003 (leftmost vertical dotted line), and large-scale introduction of IRS and LLINs in January 2006 (rightmost vertical dotted line).