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Objective: To determine whether routine surveys, such as the Demographic and Health Surveys (DHS), have underestimated child mortality in Malawi. Methods: Rates and causes of child mortality were obtained from a continuous-registration demographic surveillance system (DSS) in Malawi for a population of 32 000. After initial census, births and deaths were reported by village informants and updated monthly by project enumerators. Cause of death was established by verbal autopsy whenever possible. The likely impact of human immunodeficiency virus (HIV) infection on child mortality was also estimated from antenatal clinic surveillance data. Overall and age-specific mortality rates were compared with those from the 2004 Malawi DHS. Findings: Between August 2002 and February 2006, 38 617 person-years of observation were recorded for 20 388 children aged < 15 years. There were 342 deaths. Re-census data, follow-up visits at 12 months of age and the ratio of stillbirths to neonatal deaths suggested that death registration by the DSS was nearly complete. Infant mortality was 52.7 per 1000 live births, under-5 mortality was 84.8 per 1000 and under-15 mortality was 99.1 per 1000. One-fifth of deaths by age 15 were attributable to HIV infection. Child mortality rates estimated with the DSS were approximately 30% lower than those from national estimates as determined by routine surveys. Conclusion The fact that child mortality rates based on the DSS were relatively low in the study population is encouraging and suggests that the low mortality rates estimated nationally are an accurate reflection of decreasing rates.
We set up a continuous-registration demographic surveillance system (DSS), covering a population of 32 000, in Karonga district (northern Malawi) in 2002.15 An initial house-to-house census (baseline census) recorded personal identifiers and sociodemographic data for all individuals, and economic data and physical location for every household. Demographic surveillance was started in 230 geographically-defined clusters, each containing 15–60 households, immediately after completion of the baseline census in a given cluster. Within each cluster, one village informant was trained to record births, deaths and migrations. Project field staff followed up and recorded births and deaths monthly and migrations annually. To check completeness of infant death registration, all babies whose birth was recorded in the DSS and who were not known to have died or migrated out of the area were visited at 12 months of age. This follow-up visit detected only one extra infant death among 662 eligible babies. The total DSS population was re-censused after 2 years. This showed that the monthly and annual reporting system had registered 99% of deaths, 97% of births and 92% of migrations.15 This report includes data from the beginning of the DSS in August 2002 until February 2006. Although the initial protocol was limited to live births, fetal deaths were also reported. To encourage reporting of early infant deaths, from March 2003 village informants were asked to report fetal deaths routinely, including miscarriages (fetal death before 7 months of gestation) and stillbirths (babies born dead after 7 months of gestation). Verbal autopsy interviews were conducted, if consent was given, by a medical assistant in the local language (Chitumbuka) with the most immediate caregiver who could be traced. Interviewers used standard semistructured questionnaires developed for neonatal deaths (ages 0–28 days) or child deaths (ages 29 days–14 years). Both instruments were similar to the INDEPTH verbal autopsy tool,16 an adaptation of the World Health Organization (WHO) verbal autopsy questionnaire.17 Additionally, whenever available, patient-held health documents were reviewed together with any hospital records for children for whom the cause of death was unclear from other information. Three individuals (physicians or experienced clinical officers) independently reviewed each verbal autopsy to assign the likely underlying cause of death. Any information on maternal HIV infection status from other research studies was made available to the reviewers. In accordance with WHO verbal autopsy standards,18 HIV/AIDS was assigned as a cause of death if symptoms suggested immunosuppression in the absence of other obvious causes, taking into account any available information on maternal HIV infection or AIDS death and any prior diagnoses of suspected HIV infection. Discrepantly-coded cases were discussed and resolved if possible, or coded as “nonspecifiable” if consensus could not be reached. HIV status was not routinely determined during the study. We estimated the number of children born to HIV-infected mothers in the study population and applied the probabilities of death in this group found in other studies without antiretroviral therapy (ART) or cotrimoxazole.19–22 Unlinked anonymous HIV serosurveillance was done at two antenatal care clinics within the DSS area.23–25 Birth registration in the DSS included information on antenatal clinic attendance; this information allowed us to estimate the proportion of mothers who attended these two clinics. Antenatal clinic registers showed that the rates of attendance varied little with time, so we assumed the pattern of antenatal clinic access was the same before the start of demographic surveillance. Maternal HIV infection rates were estimated from the age-specific HIV infection prevalence at the two antenatal clinics, applied to the mother’s age group at the time of giving birth. Maternal HIV prevalence was approximately 11% at the larger clinic and approximately 7% at the smaller, more rural clinic. Prophylaxis to prevent mother-to-child transmission was not generally available during the study period, but 44 HIV+ women identified at one of the antenatal clinics in another study received the maternal and paediatric dose of nevirapine. The free national ART programme started in June 2004, with the first clinic opening in Karonga district in June 2005, 80 km from the study area. At that time children were only treated at specialized facilities. No pregnant women were started on ART during this period, making it unlikely that vertical transmission and HIV-related infant mortality were reduced by ART roll-out. Cotrimoxazole prophylaxis became available in ART clinics in late 2005, but it is unlikely that any children in the study population had received this by February 2006. Overall and cause-specific mortality rates were calculated. Observation time for each child began when the child was first seen in the baseline census, at birth or at the time of migration into the area after the baseline census. Observation time ended at the time of death (if the child was still a member in a household in the area at the time of death) or at the time of migration out of the surveillance area. Multiple episodes of observation and gaps were allowed if the child moved out of the surveillance area and later returned. All analyses were done with Stata 10.0 software (Stata Corporation, College Station, United States of America). To estimate AIDS mortality, the failure event was death from AIDS or “tuberculosis or AIDS”. Deaths from all other known or unknown causes were censored. To estimate non-AIDS mortality, the failure event was death from causes other than AIDS or “tuberculosis or AIDS”. Deaths from AIDS or from “tuberculosis or AIDS” were censored, along with deaths from unknown causes. Standard child mortality indicators were calculated from the Kaplan–Meier function as the cumulative risks of death at the age of 28 days, 12 months, 24 months, 5 years and 15 years. The probability of dying between ages x and [x + n] (known as nqx) was calculated from the Kaplan–Meier survival function as This yielded the risk of death before the age of [x + n], conditional on having survived to age x. The completeness of ascertainment of deaths was assessed from the distribution of age at death. Stillbirths were included, since stillbirths and early infant deaths were more likely to be missed than deaths of older children26–29 and the number of stillbirths was expected to exceed the number of neonatal deaths in the population.29 Overall and age-specific mortality rates were compared with those estimated by the 2004 Malawi DHS.30
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