The test case

Dengue cases are being under-reported. How will bad data help Delhis response?

According to the Municipal Corporation of Delhi,only three people have died of dengue so far this year. Indeed,only 1,370 have been diagnosed,they say. But that,as almost every resident of Delhi suspects,is a formidable under-counting. We have no clear idea what the actual incidence of the fever is. It now seems clear how this problem has arisen. The corporation reports only those cases that have been confirmed as having had dengue through the use of a particular test: IgM-capture enzyme-linked immunosorbent assay,dashingly abbreviated Elisa. The government already has Elisa tests on hand,and so they are whats offered to patients in government hospitals.

But Elisa tests have a long turnaround time,and so most private patients,who have the option,use the NS-1 antigen test instead. NS-1 gives you results in a fraction of the time that Elisa takes; nor is it completely out of reach of most patients,as it costs around Rs 400. The MCD says that it is too late this year to switch over to the NS-1 test in government hospitals. Presumably,the cost was a factor,too.

But that does not explain why the MCD did not adjust for the numbers of NS-1 tests in its figures. This is not simply a question of demanding truth from ones government. Nor is it merely indignation that,in the under-reporting,the MCD can somehow claim that the problem is less severe than it actually is. There is an even deeper concern: in public health scares of this sort,a quick response is frequently essential. Patterns will be buried in the reported cases: who got what where? Do some areas have more virulent cases? These are important epidemiological questions,especially when an outbreak appears to be gaining in strength,and a response needs to be nimble and light-footed. Yet the MCD appeared content to under-report. It is not certain,therefore,that the nature and scope of this spate of dengue cases was being analysed at all. Reportedly,the MCD will consider introducing the faster test for next year. Thats important. But its also important for the corporation,and for the Delhi government,to actually have that necessary data,so whatever efforts are needed to combat or contain the seasons dengue are properly directed.