Climate prediction of El Niño malaria epidemics in north-west Tanzania.

BACKGROUND: Malaria is a significant public health problem in Tanzania. Approximately 16 million malaria cases are reported every year and 100,000 to 125,000 deaths occur. Although most of Tanzania is endemic to malaria, epidemics occur in the highlands, notably in Kagera, a region that was subject to widespread malaria epidemics in 1997 and 1998. This study examined the relationship between climate and malaria incidence in Kagera with the aim of determining whether seasonal forecasts may assist in predicting malaria epidemics. METHODS: A regression analysis was performed on retrospective malaria and climatic data during each of the two annual malaria seasons to determine the climatic factors influencing malaria incidence. The ability of the DEMETER seasonal forecasting system in predicting the climatic anomalies associated with malaria epidemics was then assessed for each malaria season. RESULTS: It was found that malaria incidence is positively correlated with rainfall during the first season (Oct-Mar) (R-squared = 0.73, p < 0.01). For the second season (Apr-Sep), high malaria incidence was associated with increased rainfall, but also with high maximum temperature during the first rainy season (multiple R-squared = 0.79, p < 0.01). The robustness of these statistical models was tested by excluding the two epidemic years from the regression analysis. DEMETER would have been unable to predict the heavy El Niño rains associated with the 1998 epidemic. Nevertheless, this epidemic could still have been predicted using the temperature forecasts alone. The 1997 epidemic could have been predicted from observed temperatures in the preceding season, but the consideration of the rainfall forecasts would have improved the temperature-only forecasts over the remaining years. CONCLUSION: These results demonstrate the potential of a seasonal forecasting system in the development of a malaria early warning system in Kagera region.

The impact of endemic and epidemic malaria on the risk of stillbirth in two areas of Tanzania with different malaria transmission patterns.

BACKGROUND: The impact of malaria on the risk of stillbirth is still under debate. The aim of the present analysis was to determine comparative changes in stillbirth prevalence between two areas of Tanzania with different malaria transmission patterns in order to estimate the malaria attributable component. METHODS: A retrospective analysis was completed of stillbirth differences between primigravidae and multigravidae in relation to malaria cases and transmission patterns for two different areas of Tanzania with a focus on the effects of the El Niño southern climatic oscillation (ENSO). One area, Kagera, experiences outbreaks of malaria, and the other area, Morogoro, is holoendemic. Delivery and malaria data were collected over a six year period from records of the two district hospitals in these locations. RESULTS: There was a significantly higher prevalence of low birthweight in primigravidae compared to multigravidae for both data sets. Low birthweight and stillbirth prevalence (17.5% and 4.8%) were significantly higher in Kilosa compared to Ndolage (11.9% and 2.4%). There was a significant difference in stillbirth prevalence between Ndolage and Kilosa between malaria seasons (2.4% and 5.6% respectively, p < 0.001) and during malaria seasons (1.9% and 5.9% respectively, p < 0.001). During ENSO there was no difference (4.1% and 4.9%, respectively). There was a significant difference in low birthweight prevalence between Ndolage and Kilosa between malaria seasons (14.4% and 23.0% respectively, p < 0.001) and in relation to malaria seasons (13.9% and 25.2% respectively, p < 0.001). During ENSO there was no difference (22.2% and 19.8%, respectively). Increased low birthweight risk occurred approximately five months following peak malaria prevalence, but stillbirth risk increased at the time of malaria peaks. CONCLUSION: Malaria exposure during pregnancy has a delayed effect on birthweight outcomes, but a more acute effect on stillbirth risk.

Birth outcomes in adolescent pregnancy in an area with intense malaria transmission in Tanzania.

BACKGROUND: Although the effects of malaria for the mother and young baby are well described in developing countries, there is very little data on the consequences for adolescent pregnancies. This paper analyses birth outcome in adolescent pregnancy in an area of Tanzania with intense malaria transmission. METHODS: A cross-sectional descriptive analysis of 528 adolescents and 1,156 adults, malaria prevalence, and birth weight outcomes for women delivering in Kilosa Hospital between June 2001 and October 2002. RESULTS: This area has high malaria transmissions with some seasonality. Adolescent primigravidae had higher parasite prevalence than adolescent secundigravidae (41.3% versus 28.1%, p > 0.05), and than adult primigravidae (41.3% versus 31.5%, p = 0.007). Low birth weight prevalence was highest among adolescents delivering during the malaria season (odds ratio 1.7, 95% CI 1.1-2.6, p = 0.02), and was double that of adult primigravidae (31.5% versus 15.9%, p = 0.021). The prevalence of parasitemia (p = 0.003) and low birth weight (p = 0.033) declined with increasing age amongst adolescent primigravidae. Adjusted logistic regression showed a 1.4-fold increased risk of low birth weight amongst adolescents (95% CI, 0.98-1.96). CONCLUSIONS: Failure to prioritize adolescent malaria will seriously limit the success of malaria control programs in pregnancy.

Impact of El Niño and malaria on birthweight in two areas of Tanzania with different malaria transmission patterns.

BACKGROUND: Malaria infection increases low birthweight especially in primigravidae. Malaria epidemics occur when weather conditions favour this vector borne disease. Forecasting using the El Niño Southern Oscillation (ENSO) may assist in anticipating epidemics and reducing the impact of a disease which is an important cause of low birthweight. The aim of the present study was to determine the impact of the malaria epidemic in East Africa during 1997-1998 on birthweights in two different areas of Tanzania and to explore ESNO's potential for forecasting low birthweight risk in pregnant women. METHOD: A retrospective analysis of birthweight differences between primigravidae and multigravidae in relation to malaria cases and rainfall for two different areas of Tanzania: Kagera, which experiences severe outbreaks of malaria, and Morogoro which is holoendemic. Birthweight and parity data and malaria admissions were collected over a 10-year period from two district hospitals in these locations. RESULTS: The risk of delivering a low birthweight baby in the first pregnancy increases approximately 5 months following a malaria epidemic. An epidemic of marked reduced birthweight in primigravidae compared with multigravidae occurred, related to the ENSO of 1997-1998. In Kagera this birthweight difference and the risk of low birthweight were significantly lower compared with Morogoro, except after the ENSO when the two areas had similar differences. No significant interaction was noted between secundigravidae and any of the risk periods. The results indicate that the pressure of malaria is much greater on pregnant women, especially primigravidae, living in the Morogoro location. CONCLUSIONS: Surveillance of birthweight differences between primigravidae and multigravidae is a useful indicator of malaria exposure.