Dengue Spreads In India
JUST because statistics are official does not mean they can be trusted. Take India, where official reported cases of dengue fever look hopelessly inadequate. The disease, spread by mosquitoes, produces symptoms that can include fever, joint pain, exhaustion and, in a minority of cases, fatal haemorrhages. Dengue is a growing threat to public health in much of the tropics, and is thought to kill at least 20,000 people a year, while infecting many millions more. India suffers particularly from dengue, especially at this time of year, after the end of its summer monsoon, when puddles of still water in cities become breeding grounds for the Aedes mosquito, the vector responsible for spreading the illness.
Judge by newspaper reports of dengue infection and deaths, or by word-of-mouth among residents who succumb to the illness in Delhi, for example, and it is clear that this is a pretty common affliction. Yet official reports of dengue in India suggest only some 20,500 cases a year, in a population of more than 1.2 billion people. The gap is worryingly large between the official data—which present dengue as a negligible problem—and the common perception that the disease is a widespread threat. For the sake of holding a mature public debate about the disease, its toll on human life and its wider economic burden, far better statistics are needed.
A new report, published on October 7th, gives the first clear sense of how wrong the official data may be, and makes a stab at producing reliable statistics. Researchers from America and India, led by Donald Shepard of Brandeis University, conclude that the burden of dengue in India is the heaviest in the world. Rather than 20,000 annual cases, they estimate that 5.8m Indians suffer from dengue every year. Their estimate is 282 times greater than the official one.
Is it credible? Professor Shepard calls the study robust, says he is “confident” in the “solid” methodology used and points to consistency between the Indian study and similar ones done recently in other countries. The final figure is entirely plausible. The researchers, over three years, assessed patients admitted to hospital with the disease in a district of Tamil Nadu, included surveillance data from 18 other states, and analysed the medical records of dengue patients in ten public and private hospitals. He and his fellow researchers concluded that not only is the far larger figure reliable, but also that they have evidence dengue is a worsening problem in India, probably as a result of rapid urbanisation. More people crammed ever closer together are more likely to pass along the disease.
Why official data so seriously underestimate the dengue burden is no mystery. Two types of test exist for the disease’s diagnosis (beyond the mere assessment of its symptoms). One is rapid, cheap and applied in the first five days after infection. Known as NS1, it is used widely by patients and doctors. But officials do not accept NS1 as evidence of dengue, allowing only the results of a more cumbersome laboratory test, which detects antibodies against dengue. As that is more rarely used, it is unsurprising that relatively few patients are officially diagnosed as having dengue. Mr Shepard points out that other countries (such as America) publish official data of both confirmed and suspected cases of dengue, a practice that India might adopt.
India is not alone in suffering from dengue. Brazil, for example, endures high rates of infection, and the disease is a threat in much of the rest of South and South-East Asia. But the high and growing burden in India suggests a pressing need to improve its public health efforts. The researchers also attempt to estimate the economic cost of dengue—”Money talks,” concludes Mr. Shepard—as an additional spur to policymakers to take action. They conclude that the cost of medical care for those who contract dengue is equal to nearly $550m annually. Additional economic costs, which are borne mostly by patients and their families, for example in lost income while off work, might be roughly equal to that much again. In total, they suggest, dengue already costs India over $1.1 billion each year.
More could be done to tackle the disease. One method for example, long used in Singapore, would be to remove breeding spots for the mosquitoes—by draining even small pools of water in urban areas—or to attack the vector by other means, such as insecticides. This helps, too, against other diseases spread by mosquitoes, such as malaria. A laudable effort announced last week by India’s prime minister, Narendra Modi, to “clean up” India, could yet see more done to drain standing water. Elsewhere, as in Australia and Brazil, new technology is being used to disrupt the ability of mosquitoes to pass on dengue. One of their methods has been to spread about mosquitoes which have inserted into them a bacterium taken from fruit flies. And there is work under way towards a vaccine for dengue—the study released this week was funded by a vaccine-maker, Sanofi Pasteur, though the researchers say the firm had no role in preparing or influencing their work.
How India responds to such public-health challenges is a matter of growing importance. The country’s success in eradicating polio, and a renewed enthusiasm for tackling dreadful sanitation, both suggest more capacity and greater will to address the spread of diseases. But at the same time, a large and ever more mobile population mean that illnesses are more easily spread. How India would react to a more deadly, and virulent, public-health threat—such as it would if the Ebola virus were brought into the country, by the many Indians who work in West Africa—is uncertain. Peter Piot, who helped to discover Ebola, says the spread of Ebola to India is a great worry. One starting point for addressing any public-health problem—whether dengue, Ebola or anything else—is with the gathering and publishing of accurate data about it. If India can improve its record on this count, so much the better.
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