Global Malaria Estimates Are Reduced
By LAURA BLUE Tue Sep 23, 3:50 AM ET - TIME
The World Health Organization (WHO) has cut its global estimate of yearly malaria cases by more than 100 million, according to a report released Thursday by the health agency. Almost all of that downward revision was attributable to updated surveillance numbers - mostly in Asia, and particularly in
The last World Malaria Report in 2005, tallied the global incidence rate at between 350 million and 500 million new cases of malaria per year. The current report downgrades that figure to 247 million. Likewise, where the last report claimed that the disease kills "more than 1 million" people each year, the 2008 update, which is based on 2006 data (the most recent numbers available), suggests that figure is now closer to 800,000.
The impact of malaria, however, is still massive. "Whether it's 200 million or 500 million [cases], that's a lot of infections with a big health burden and a big economic burden," says Bernard Nahlen, deputy coordinator of the U.S. President's Malaria Initiative - especially, he says, "for something that is treatable and to a large extent preventable. If your child's life can be saved by treatment for 50 cents, you should treat."
But the WHO's correction comes less than a year after the United Nations made a similar announcement, acknowledging last November that its AIDS-battling agency, UNAIDS, had overstated its estimates of the global HIV burden by about 6 million cases; that agency revised its numbers also based on newer and more accurate surveys. At the time, the U.N. came under fire from critics for inflating its estimates in order to exaggerate the urgency of the epidemic - and to spur bigger donations.
There may have been some truth to that argument. Money funneled to HIV and malaria control has soared in the last decade, to almost $9 billion and roughly $1 billion a year, respectively (those figures, too, are hazy estimates), although in the case of HIV especially, money has not always been channeled into disease-control programs based on the best scientific evidence. (That's particularly true for politically sensitive - and, therefore, under-funded or ignored - interventions that aim to prevent high-risk sex and drug abuse.)
In large part, such massive miscalculations have less to do with politics than with the simple fact that epidemiology involves an inordinate amount of guesswork. Routine re-evaluations of existing data often result in data shifts, sometimes huge ones, which global health experts and epidemiologists have come to expect. "If you go up to a little clinic in
The WHO ascribes most of the current revision to a reassessment of the malaria epidemic in Asia (although the vast majority of malaria cases and deaths still occur in
Epidemiologists are often described by the media as "disease detectives," who use statistical tools - carrying out the occasional survey, for example, or, in the case of malaria, using temperature and terrain maps to help predict where disease-carrying mosquitoes may live - to hunt down and eliminate global killers. The comparison is useful for another reason: Disease trackers, like crime solvers, often spend a lot of time sifting through a few, imperfect clues - hunches, really - to piece together a fuller picture. But that picture often ends up being indistinct as well. The WHO says, for example, that the "confidence interval" of its new estimate - the numerical range within which scientists believe the actual malaria incidence most likely lies - is 189 million cases to 327 million cases per year.
It is an enormous but unavoidable margin of error. Unlike in developed countries, such as the U.S., that have the infrastructure to compile more detailed population-wide medical records, disease surveillance in places like the Democratic Republic of the Congo, a large central African country with few doctors, few roads, limited medical infrastructure and a recent history of bloody conflict, is a much more difficult undertaking. Officials have trouble counting births and deaths in some regions, let alone getting a sense of how many people may have suffered from a particular disease.
What's more, even where records exist, there is usually no way to confirm their validity. Doctors in the developing world often lack lab facilities to authenticate cases of suspected malaria. Perhaps more often, they never even get to see patients who have the disease - many patients either cannot afford the time or money to see a doctor or they simply self-diagnose and take cheap over-the-counter medications to battle malaria-like symptoms. The WHO estimates that nationally reported (but often unvalidated) malaria cases account for just 40% of the global estimate; the other 60% comes from "detective work" by epidemiologists.
The fuzzy math aside, the good news is that malaria control efforts are working. The 2008 World Malaria Report singles out
But similar programs are underway across much of