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Verbal autopsy is not well suited to estimating malaria deaths
27 Oct 2010
Paul Chinnock
Source: TropIKA.net
Extensive media attention has been given to a study [1] in which use of the controversial technique of verbal autopsy (VA) has produced figures for malaria deaths very different from those arising from conventional methods. (See for example a Reuters report
.) But does the lack of agreement between two alternative approaches mean, as the study authors argue, that it is the much higher figure resulting from the use of VA that is correct?
The study, published in the Lancet, was conducted in India where, based on routine case reports, the World Health Organization estimates that there were 10,000–21,000 malaria deaths in 2006. The VA researchers estimated that there are in fact around 205,000 deaths annually – some 13 times the WHO figure.
The researchers based their conclusions on interviews by non-medical field workers with families or “other respondents” about each of 122,000 deaths occurring during 2001–2003 in randomly selected areas of India. They obtained for each case a half-page narrative, plus answers to questions about the severity and course of any fevers. The data were interpreted by physicians trained in disease coding.
Of the 75,342 coded deaths between one month and 70 years of age, 2681 (3.6%) were attributed to malaria. (Ninety per cent of malaria deaths were in rural areas and 86% occurred outside of any health-care facility.) The researchers extrapolated from these findings to calculate plausible lower and upper bounds of 125,000 and 277,000 for malaria deaths in India nationally. In their view, the true figure is likely to be around 205,000 but even the lower-bound figure is still over five times greater than the maximum figure in the WHO estimated range.
The 205,000 figure is comprised of 55,000 deaths in under-fives, 30,000 in children aged 5–14, and 120,000 in people aged 15 and older. The high proportion of adult deaths is particularly surprising, as worldwide only around 10% of malaria deaths are believed to be in adults.
The authors go on to argue that, based on their Indian findings, the global figure for malaria mortality could be much higher than current estimates, particularly as regards the number of adults who die from the disease.
The study authors have rightly pointed out that: “National malaria death rates are difficult to assess because reliably diagnosed malaria is likely to be cured, and deaths in the community from undiagnosed malaria could be misattributed in retrospective enquiries to other febrile causes of death, or vice-versa”. This is also not the first time that the accuracy of WHO mortality statistics has been questioned.
Many, however, will query the suitability of VA for estimating malaria deaths. It is well known that, in many parts of the world where malaria is endemic, any case of fever is popularly referred to as “malaria”, even though the symptoms of malaria are shared with many other common causes of acute fever. Put simply, asking a family member whether a death that took place up to three years ago involved a fever, which might have been due to malaria, seems unlikely to produce a reliable answer. (Additional information was collected by the field workers in this study but the underlying weakness of relying on the informants’ memories and personal interpretations nevertheless remains.)
WHO’s Global Malaria Programme (GMP) has already responded to the researchers’ conclusions. GMP acknowledges that “routine reports of malaria cases and deaths in India are certainly incomplete” but considers that the estimate of 205,000 deaths annually is far too high. A GMP statement continues:
“Recent work by WHO and partners in one Indian setting showed that as few as 4% of deaths attributed to malaria by VA were actually caused by malaria.
“The limitations of the new study are exposed when estimates are examined for particular states. The proposed estimate of malaria mortality in Orissa is close to the average estimated for Africa. It suggests, implausibly, that there are 1–50 million falciparum malaria cases annually in a population of 40 million.”
The last few years have seen an increasing interest in the use of VA as a public health tool, to help address the uncertainty in many parts of the developing world as to the most important causes of death. There have been studies validating some of the findings from VA surveys. However, the results of this new research can be considered to be evidence that the technique is not suitable for producing estimates of malaria mortality.
Reference
Dhingra N, Jha P, Sharma VP, Cohen AA, Jotkar RM, Rodriguez PS, Bassani DG, Suraweera W, Laxminarayan R, Peto R; for the Million Death Study Collaborators (2010). Adult and child malaria mortality in India: a nationally representative mortality survey. Lancet 2010 Oct 20 [Epub ahead of print]. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20970179
Comments
Note, however, the following commentary (published in the Lancet 20th Nov) which argues that, while verbal autopsy is an imperfect tool, the results of the study should give the Indian authorities "pause for thought" and that the country's malaria burden may have been underestimated: http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(10)61084-7/fulltext
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