Chikungunya numbers may be higher than what is officially reported as not all who show symptoms get tested.
Those who do may show false negative results if they get tested either too early or too late for diagnosis.
There are three ways of determining whether a person has chikungunya. The first is a serology test to detect antibodies produced in response to the virus.
The second is a PCR test to detect viral RNA. It is the most accurate test and can detect the infection even within 24 hours of developing symptoms.
The third is a laboratory culture of the virus that can be observed under the microscope.
“All the three tests are quite accurate and are accepted by MCD for registering a case as chikungunya,” said Dr DK Seth, director, hospital administration, north MCD.
Since PCR is a sensitive test and impossible to do at government hospitals, most of the times serology tests are done. “With the rush that the government hospitals receive, it is impossible to do a PCR test. It is expensive and time consuming,” said Seth.
However, a PCR test is taken to be confirmatory for reporting deaths due to chikungunya.
“After a person gets chikungunya, the serology test will be positive for the antibody for around two or three months. If a person has had even a mild bout of chikungunya in the last three months, and later died in the hospital because of kidney failure or liver problems, how can the serology test be accepted to say that it is a chikungunya death?” he said.
Serology tests for antibodies may also show false negative if the tests are done before a week of the symptoms appearing.
In Ganga Ram, from Sep 1-13, out of 565 samples of suspected viral fever, 319 came positive for chikungunya virus which is about 56% positivity.
“We found that serology results were returning negative but when we started performing RT-PCR it showed positive results. This could mean the number of cases in Delhi could be higher as others may also be facing the same problem,” said a doctor.
Most doctors, however, don’t prescribe tests if a patient doesn’t have co-morbid conditions such as diabetes, hypertension, kidney or liver disease.
“We usually do not prescribe chikungunya tests in patients who show symptoms of the disease. Only where we suspect chikungunya or dengue but the patient doesn’t show clear symptoms do we ask for these tests to confirm,” said Dr Srikant Sharma, senior consultant, medicine department, Moolchand Hospital.