1 Institut de Recherche pour le Développement (IRD) BP 1386 Dakar, Sénégal
2 Laboratoire Population-Environnement-Développement, UMR 151 IRDUniversité, de Provence, Marseille, France
Correspondences: Jean-François Etard, IRD, BP 1386, CP 18524 Dakar, Senegal. E-mail: etard{at}mpl.ird.fr
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Abstract |
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Methods Between 1989 and 2000, a postmortem interview was conducted using a standardized questionnaire which was independently reviewed by two physicians who assigned the probable underlying cause of death. Discordant diagnoses were discussed by a panel of physicians. Causes of death were grouped into a few categories; cause-specific mortality rates and fractions were generated.
Results Between 1989 and 1997, all-cause mortality fluctuated. Diarrhoeal diseases, malaria and acute respiratory infections explained between 30% and 70% of the mortality before 10 years of age. In children 19 years old, malaria death rate increased between 1989 and 1994 and thereafter did not change. The 19982000 years were marked by a peak in mortality, attributed to a meningitis outbreak in children more than one year old paralleled by an increase in death rate from fever of unknown origin, diarrhoeal diseases, and acute respiratory infections in children under 5 years.
Conclusions Verbal autopsy provided useful information on the mortality structure responsible for the 19982000 peak in mortality. It underlined that, outside outbreak situations, malaria was a leading cause of death for 19 year old children and that diarrhoea, acute respiratory infections, or fever from unknown origin accounted for up to 50% of the deaths among the children under 5 years.
Accepted 14 May 2004
Medically certified information is not available for at least 70% of the worldwide deaths. In rural settings of developing African countries, vital registration infrastructure is poor, access to health centres with adequate diagnosis facilities limited and most childhood deaths occur at home. Reliable medical information on causes of death is therefore lacking and other sources of data must be used to estimate cause-specific mortality. Data from population monitoring laboratories conducting postmortem interviews with relatives of the deceased person to ascribe causes of death, so-called verbal autopsies, are one of the alternative sources.14 This method is most valid for diseases with well-defined symptoms recognizable by the local population, such as neonatal tetanus, measles, malnutrition and less so for diseases with shared symptoms, such as malaria and acute respiratory infections.5 Despite these limitations, its use within research settings and validation studies have been encouraged. In sub-Saharan Africa, verbal autopsy in childhood deaths has been applied in Kenya, Ethiopia, Congo, Tanzania, Liberia, The Gambia, and South Africa.612 In these settings only a few diseases account for most of the deaths and, for purpose of planning, it may be sufficient to identify major causes of death. In Senegal, it has been used in the two rural areas of Bandafassi (8000 inhabitants, 19841993) and Mlomp (6300 inhabitants, 19851989).13,14 The same approach has been used since 1983 in the rural study zone of Niakhar, but leading causes of death among under-5 children have only been briefly described for the period 19831986.15 We report here total and cause-specific death rates before 15 years of age for leading causes of death attributed by verbal autopsy and trends over a 12-year period, 19892000.
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Population and Methods |
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Assignment of probable cause of death by verbal autopsy procedure
A standardized questionnaire, initially developed at ICCDR-B in Bangladesh, was completed by a lay reporter in local language.22,23 The current version is a 15-page questionnaire available on the IRD website (http://www.ird.sn/activites/niakhar/). It comprised several parts: identification, use of health services preceding the fatal illness, open text and closed questions to record the actual history and the symptoms during the terminal illness, and summary sheets. Each questionnaire was reviewed independently by two clinicians who assigned the most likely cause of death based on their own medical judgement. Discordant diagnoses were discussed by the panel of clinicians involved in Niakhar and a consensus cause was searched. If a consensus was not reached, the death was categorized as ill-defined/unknown. Three-digit International Classification of DiseaseNinth Revision (ICD-9) codes were used. For general symptoms (code 780), the fourth digit was used. Based on the ICD-9 codes assigned, causes of deaths were aggregated into five broad categories, diarrhoeal diseases, acute respiratory infection (ARI), meningitis, malaria, fever of unknown origin (FUO), in addition to ill-defined/unknown causes and other causes (Table 1). During the 1980s and 1990s, measles and pertussis vaccine trials and adequate case management have led to a precise ascertainment of deaths due to these infections and a dramatic reduction in their incidence.19,20 The local epidemiological context (outbreaks, known seasonality in incidence) has been used as a piece of information. When an outbreak of cholera, meningitis, or shigellosis was notified after the bacteriological confirmation of the first cases, subsequent deaths matching the clinical case definition were attributed to the outbreak. In the case of an acute fever with convulsions or impaired consciousness, unphased seasonal incidences of malaria and epidemic meningococcal disease (humid season versus dry season) have been used to help in distinguishing between these two aetiologies. When the child had a history of fever and respiratory signs (cough, chest pain, expectoration, fast breathing) with no convulsions during the dry season, a death due to an acute respiratory infection (ARI) was accepted. When it was impossible to assign the underlying cause in front of a febrile illness with respiratory distress during the malaria season, the death was categorized as fever from unknown origin (FUO). In developing countries, more than 50% of the deaths due to diarrhoea, ARI, malaria, and other infectious diseases are attributed to underweight.24 Rather than attempting to group deaths due to malnutrition into a malnutrition category, we chose to classify these deaths into one of the five broad categories, depending on the terminal associated cause, or into the other causes category when malnutrition was not followed by an infectious disease. The number of deaths due to measles was so low that measles death rates are not presented here but can be found elsewhere.19
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The DSS design has been approved by Ministry of Health and Regional health authorities.
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Results |
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All-cause mortality
Neonatal mortality (028 days) declined over the study period from 40/1000 lbirths in 19891991 to 24/1000 lbirths in 19982000.
Infant mortality, 80/1000 lbirths on the average between 1989 and 1997, with a decreasing trend, increased abruptly in 1998 to 100/1000 lbirths (Figure 1).
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In the older age groups (59, 1014), mortality remained between 15 and 35/1000 before increasing abruptly in 1998.
The high level of mortality observed in 1998 started to decline in 1999.
Effect of gender on mortality
Over the study period, infant mortality among boys was larger than in girls (90 versus 75/1000 lbirths, RR = 1.19 [95% CI: 1.07, 1.33], P = 0.001). This effect was significant during the neonatal period (38 versus 28/1000 lbirths, RR = 1.36 [95% CI: 1.14, 1.63], P < 0.001) and the post-neonatal period (89 versus 75/1000 children alive at day-29, RR = 1.18 [95% CI: 1.06, 1.32], P < 0.01). No effect of gender in the other age groups/periods reached statistical significance.
Cause-specific mortality
Neonatal deaths (n =484)
More than 90% of these deaths were related to a cause different from the five broad categories with almost 60% linked to prematurity or perinatal infection.
Before one year old (n = 1200)
Since neonatal deaths accounted for 40.3% of these deaths, a large mortality fraction due to other causes was observed. Over the whole study period, diarrhoeal diseases and ARI accounted for 30% of the infant mortality and malaria for 10%. In term of rates, compared with 19951997, an increase in mortality rate from FUO (IRR = 4.8; 95% CI: 2.4, 10.6), diarrhoeal disease (IRR = 1.9; 95% CI: 1.3, 2.9), and ARI (IRR = 1.5; 95% CI: 0.96, 2.4) was noticed in 19982000, while death rate from other causes tended to decline (IRR = 0.8; 95% CI: 0.6, 1.0) (Table 2).
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Between 59 years old (n = 340)
Until 1998, malaria and diarrhoea predominated, explaining respectively 46% and 13% of the mortality. As in the 14 year age group, the malaria death rate increased during 19891991 and 19921994 (RR = 2.6; 95% CI: 1.4, 5.0) and then did not change significantly until 1998. The proportion of deaths due to malaria paralleled this pattern. A major feature in this age group was the dramatic increase in the death rates attributed to meningitis and FUO during the period 19982000 compared with 19951997 (IRR = 56.5; 95% CI: 9.7, 2273.3 and IRR = 10.6; 95% CI: 2.6, 93.3, respectively) (Table 2).
Between 1014 years old (n = 142)
Due to the low number of deaths in this age group, the mortality pattern should be interpreted cautiously, but diarrhoea remained a leading cause. As in the younger age groups, the period 19982000 was marked by a high mortality rate due to meningitis and FUO compared with the preceding period (IRR incalculable due to zero case in 19941997; rates changed from 0 to 2.33 deaths/1000 p-y and from 0 to 1.12 deaths/1000 p-y, respectively) (Table 2).
Seasonality of causes of death
Throughout the whole study period, two-thirds of deaths occurred during the second semester of the year with a maximum in SeptemberOctober (16% and 18%, respectively). This distribution was observed for diarrhoea, ARI, FUO, ill-defined/unknown, and other causes. The months from February to April concentrated two-thirds of the meningitis deaths, and 92% of deaths attributed to malaria occurred during the second semester with a peak in SeptemberOctober (26% and 31%, respectively). The peak in ARI deaths occurred later in OctoberNovember (Figure 2).
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Discussion |
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Trends in causes of death before 1998
In spite of these limitations, verbal autopsy provided useful information on the major causes of death and trends. Among the children under 5 years old, diarrhoea and ARI accounted for up to a third of the mortality and FUO remained around 5%. For children between 19 years old, malaria was the leading cause of death, explaining a third of the mortality. A recent meta-analysis of verbal autopsy data on malaria mortality in children under 5 for the period 19821998 in West Africa using a modelling approach to correct misclassification yielded an average rate of 7.8 deaths/1000 child-years between 1982 and 1998.35 The estimate in Niakhar between 1989 and 1997 was 9.9/1000. This meta-analysis also showed an increase in the proportion of malaria deaths from 18% to 23% between 19821989 and 19901998. In our study in rural Senegal, the same trend, although more pronounced (1936%), was observed between 19891991 and 19921998. Another modelling approach to ARI mortality provided estimates of the CSMF as a function of the under-5 mortality.36 Applied to the mortality level observed in Niakhar, one could expect between 20% and 25% of deaths due to ARI, while only 10% on the average were observed. When compared with data from rural Gambia, the underestimation seemed to affect primarily the first year of life.11 A number of ARI deaths are likely to have been classified in another category, such as FUO or other causes, due to overlapping symptoms.
19982000 mortality
Verbal autopsy was useful in revealing the structure by cause of the 19982000 mortality. The large meningitis mortality fraction (>40%) among 514 year old children in 19982000 is clearly linked to the major West African meningitis outbreak which struck Senegal in 19981999 with 2700 notified cases between October 1998 and February 1999.37 The first cases were observed in the study zone as soon as February 1998, and an immunization campaign was then launched by the regional health authorities. Verbal autopsy revealed a posteriori that meningitis was not the sole responsible cause of the 19982000 mortality peak, particularly among infants. An increase in death rates due to diarrhoea and ARI among the 05 year olds, and due to FUO in every age group paralleled the meningitis outbreak. The increase in the number of deaths due to diarrhoea could partly be explained by an outbreak of shigellosis which affected the study zone in 1999 with a case fatality rate of 7%.38 The increase in death rate due to FUO could be explained by the meningitis outbreak, the signs of the fatal illness being partially reported by the relatives and the death misclassified. Indeed, the proportion of deaths due to FUO was significantly higher during the meningitis outbreak period than the rest of the year, and then only for the period 19982000. In that case, the number of deaths due to meningitis has been underestimated.
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Conclusion |
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KEY MESSAGES
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Acknowledgments |
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References |
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