Malaria deaths 'higher than expected'

“Malaria deaths twice as high as was thought,” The Independent has reported today. Many newspapers have covered research that found that malaria claimed 1.2 million lives worldwide in 2010. The Guardian also reveals that the study “demolishes conventional thinking” that almost all malaria deaths are in babies and small children under the age of five.

Malaria-related deaths in the UK were not examined in this study. Malaria is not generally present in the UK, but this preventable disease is commonly contracted by unprepared travellers visiting tropical and subtropical regions. In recent years, newspapers have reported several cases of high-profile people who have caught malaria, including pop star Cheryl Cole and Premiership footballer, Didier Drogba.

The headlines are based on a disease-modelling study that examined a large database, alongside a systematic review of other studies, to identify deaths due to malaria across 105 countries over the past 30 years. The research found that malaria in 2010 was the cause of death for 1.2 million individuals, including 714,000 deaths in children younger than five years and 524,000 in individuals aged five years or older. The results tend to show an increase in mortality from 1980 to peak levels in 2004, but since then a clear decline.

The researchers say that the recent decrease in malaria mortality in Africa in particular is due to an increase in measures to control the disease, which has been supported by international help. They say that support from international donors needs to increase if malaria is to be eradicated.

However, the primary aim of this study was to predict trends over time in malaria mortality, not to try to find causes for malaria mortality or to examine the effectiveness of different solutions to the problem.

Where did the story come from?

The study was carried out by researchers from the University of Washington, Seattle, and the University of Queensland in Australia, and was funded by The Bill & Melinda Gates Foundation.

It was published in the peer-reviewed medical journal The Lancet. The papers accurately reflected the findings of the research.

What kind of research was this?

This was a modelling study that involved collecting all available data on malaria mortality between 1980 and 2010. During the past 10 years, efforts to tackle malaria have increased. This study aimed to assess the trends in malaria mortality in order to check the progress of these efforts, and to identify areas that need future attention. To do this, the researchers developed a range of models to estimate mortality by age, sex, country and year.

What did the research involve?

As part of the Global Burden of Disease 2010 Study, all available data for mortality by cause from 1980 to 2010 are being systematically collated, and the researchers used this along with the Malaria Atlas Project (MAP). The MAP monitored the levels of transmission of Plasmodium falciparum (the parasite that causes the most severe form of malaria) in different countries.

The researchers describe how they used a large database to identify systematically all data for deaths classified as due to malaria. The researchers restricted their analyses to 105 countries that had information on malaria transmission during the 30-year period of interest. For countries that had eliminated malaria during this period, they identified the year of elimination and estimated the number of malaria deaths for the period when transmission was still occurring.

The researchers supplemented the information identified with a search of the global literature to identify published and unpublished ‘verbal autopsy’ studies. These record the probable cause of death based on the deceased's symptoms and likely medical diagnosis. They were population-based studies that covered a period of at least one year and provided the number of deaths by cause according to verbal autopsy. The verbal autopsy method tends to be used in countries that lack a formal and reliable system for registering deaths.

In order to develop their models they divided the world into three groups:

countries from sub-Saharan Africa and Yemen (45 countries)
countries outside of sub-Saharan Africa (45 countries)
countries with only Plasmodium vivax malaria (15 countries)

Malaria deaths in countries that only have Plasmodium vivax malaria are lower than others, so for these countries the researchers simply modelled malaria death rate by age. For the other 90 countries the researchers tested different predictive models, including:

looking separately by sex
looking separately by age group (less than five years and five years and older)
looking at the transmission intensity of Plasmodium falciparum malaria, which is a key predictor of the number of malaria deaths

What were the basic results?

The study provides extensive mortality data by country. Overall, the researchers observe a fluctuation in the number of malaria deaths worldwide over the 30-year period:

995,000 deaths in 1980 (95% confidence interval CI 711,000 to 1,412,000)
a peak level of 1,817,000 deaths in 2004 (95% CI 1,430,000 to 2,366,000)
a decrease to 1,238,000 deaths in 2010 (95% CI 929,000 to 1,685,000)

In Africa there were:

493,000 deaths in 1980 (95% CI 290,000 to 747,000)
an increase to 1,613,000 in 2004 (95% CI 1,243 000 to 2,145,000)
about a 30% decrease to 1,133,000 in 2010 (95% CI 848,000 to 1,591,000)

Outside of Africa, malaria deaths have steadily decreased:

502,000 in 1980 (95% CI 322,000 to 833,000)
down to 104,000 in 2010 (95% CI 45,000 to 191,000)

The researchers suggest that there have been more deaths in people aged five years or older than previous studies have estimated. In 2010 there were 435,000 deaths in over-fives in Africa (95% CI 307,000 to 658,000) and 89,000 deaths in over-fives outside of Africa (33,000–177,000). The comparative 2010 figures for under-fives are 699,000 deaths (95% CI 415,000 to 1,112,000) in Africa and 15,000 deaths (95% CI 4,300 to 31,000) outside of Africa.

Deaths in both under- and over-fives have been decreasing over the past five years. However, the trend of deaths for countries within Africa is different from that for countries outside Africa: in Africa deaths have declined in both the under- and over-fives in the past five years, though deaths in the under-fives still remain clearly higher than those in the over-fives; outside of Africa deaths in both age groups have also steadily declined, though here the mortality rate in the over-fives is higher than in under-fives.

How did the researchers interpret the results?

The researchers conclude that their findings show that the global malaria mortality burden is larger than previously estimated, especially in adults. They say that the recent decrease in malaria mortality in Africa is due to more measures being taken to control the disease, which has been supported by international help. However, they say that support from international donors needs to increase if malaria is to be eradicated.

Conclusion

This study has looked at a large amount of data and used systematic methods to examine trends in malaria mortality over the past 30 years. It shows that malaria in 2010 was the cause of death for 1.2 million individuals, including 714,000 deaths in children younger than five years and 524,000 in individuals aged five years or older. The results tend to show an increase in mortality from 1980 to peak levels in 2004, but since then a clear decline.

The researchers say that the recent decrease in malaria mortality in Africa in particular is due to malaria control activities being increased, supported by international help. They say that support from international donors needs to increase further if malaria is to be eradicated.