Nearly 300 times as many people are hospitalized with severe dengue infections in India as are officially reported by the government, according to a study published this week.
The study of the mosquito-borne disease, by researchers at Brandeis University in Massachusetts, is part of a growing body of literature demonstrating that no other country in the world suffers as many dengue infections as India.
Officially, the Indian government reports that an average of about 20,000 people are hospitalized annually with dengue infections. The Brandeis study suggests that the real number of hospitalizations is closer to six million, and other studies have suggested that the actual number of Indians infected annually is probably more than 30 million.
“In absolute numbers of cases, we estimate that India has the highest absolute number of cases,” Dr. Donald S. Shepard of Brandeis, a co-author of the study, said in an interview.
The study estimated that the direct and indirect costs of these hospitalizations exceeded $1 billion annually. The Brandeis study was funded by Sanofi Pasteur, the pharmaceutical company, which is in the midst of trials of a dengue vaccine. Sanofi Pasteur has a financial interest in suggesting that dengue’s reach and costs are high, but investigators said Sanofi Pasteur had no control over the conduct of the research.
The study’s methodology, which focused on only one state in its clinical assessments and included broad assumptions about how patients seek care and are tested for the virus, probably underestimated the actual burden of the disease, Dr. Shepard said.
Government officials have long acknowledged that official data vastly underestimates the burden of the illness, but they explain that any change in the system would impede year-to-year comparisons. That the annual dengue epidemic coincides with the beginning of India’s busiest tourist season may also play a role in the government’s decision-making.
Experts have long complained that India’s underestimating of the disease’s vast reach impedes its people from taking preventive measures, discourages efforts to clean up the sources of the disease and slows research efforts for a vaccine. For 80 percent of those infected, dengue causes only mild symptoms of fatigue and a brief fever. The remaining 20 percent may be affected by more serious flulike symptoms, with high fever, vomiting, searing pain behind the eyes, rash, and muscle and joint aches that can be so intense that the illness has been called “breakbone fever.”
The acute part of the illness generally passes within two weeks, but symptoms of fatigue and depression can linger for months. In about 1 percent of cases, dengue advances to a life-threatening cascade of immune responses known as hemorrhagic or shock dengue.
This potentially fatal condition generally happens only after a second dengue infection. There are four strains of the dengue virus, and infection with a second strain can fool the immune system, allowing the virus to replicate. When the body finally realizes its mistake, it floods the system with so many immune attackers that they are poisonous. Such patients must be provided intravenous fluids and round-the-clock care to avoid death.
The first isolation of dengue in India occurred in Calcutta, now Kolkata, in 1945, and the first epidemics in India were reported in the 1960s. Many researchers say dengue is now so endemic that nearly all Indians are infected at some point in their lives, often several times.