Malaria transmission in Bissau, Guinea-Bissau between 1995 and 2012: malaria resurgence did not negatively affect mortality

Abstract

Introduction: As Plasmodium falciparum prevalence decreases in many parts of Sub-Saharan Africa, so does immunity resulting in larger at risk populations and increased risk of malaria resurgence. In Bissau, malaria prevalence decreased from ∼50% to 3% between 1995 and 2003. The epidemiological characteristics of P. falciparum malaria within Bandim health and demographic surveillance site (population ∼100,000) between 1995 and 2012 are described.

Methods and findings: The population was determined by census. 3603 children aged <15 years that were enrolled in clinical trials at the Bandim health centre (1995-2012) were considered incident cases. The mean annual malaria incidence per thousand children in 1995-1997, 1999-2003, 2007, 2011, 2012 were as follows; age <5 years 22→29→4→9→3, age 5-9 years 15→28→4→33→12, age 10-14 years 9→15→1→45→19. There were 4 campaigns (2003-2010) to increase use of insecticide treated bed nets (ITN) amongst children <5 years. An efficacious high-dose chloroquine treatment regime was routinely used until artemisinin based combination therapy (ACT) was introduced in 2008. Long lasting insecticide treated bed nets (LLIN) were distributed in 2011. By 2012 there was 1 net per 2 people and 97% usage. All-cause mortality decreased from post-war peaks in 1999 until 2012 in all age groups and was not negatively affected by malaria resurgence.

Conclusion: The cause of decreasing malaria incidence (1995-2007) was probably multifactorial and coincident with the use of an efficacious high-dose chloroquine treatment regime. Decreasing malaria prevalence created a susceptible group of older children in which malaria resurged, highlighting the need to include all age groups in malaria interventions. ACT did not hinder malaria resurgence. Mass distribution of LLINs probably curtailed malaria epidemics. All-cause mortality was not negatively affected by malaria resurgence.

Figure 1. Monthly incidence of P. falciparum malaria per 1000 children aged less than 15 years attending the Bandim Health Centre and monthly rainfall (mm).

Total monthly rainfall is shown as columns. Monthly P. falciparum incidence is shown as a line. Vertical arrows idicate when ITN or impregnation campaigns aimed at children <5 years of age were conducted. Horizontal arrows indicate the periods when artemisinin based combination therapy (ACT) and long lasting insecticide treated bed nets (LLIN) have been in use.

Figure 2. Annual malaria incidence and mortality per 1000 children aged less than 1 (A), 1–4 (B), 5–9 (C) and 10–14 years (D).

Annual malaria incidence is shown as columns. Annual all-cause mortality is shown as a line.

Figure 3. The annual proportion of children aged less than 5, 5–9 and 10–14 years with malaria and the median age of children aged less than 15 years attending the Bandim Health Centre and diagnosed with malaria.