Doctors seeing many patients with typical dengue symptoms testing negative in Karnataka

Doctors in Karnataka are seeing many patients reporting with typical dengue symptoms, but testing negative for the vector-borne disease. While such cases are being recorded as “suspected dengue” by the Health Department, doctors have warned the public to not ignore fever and other symptoms even if they test negative.

Doctors in Karnataka are seeing many patients reporting with typical dengue symptoms, but testing negative for the vector-borne disease. While such cases are being recorded as “suspected dengue” by the Health Department, doctors have warned the public to not ignore fever and other symptoms even if they test negative.

While 4,046 suspected dengue patients were reported in the last 24 hours in the State, only 549 tested positive for dengue, including 221 in Bengaluru. Dengue has been on a steady rise in the State with 12,000 cases and eight deaths reported so far this year. Of these, 4,526 cases and one death are from Bengaluru. The number of dengue cases shot up from 6,187 on July 1 to 12,000 as of July 19, according to data from the State Health Department.

Virologist V. Ravi, who formerly headed the department of Neurovirology at NIMHANS, said this could be either due to the wrong timing of the dengue tests or prior infection.

“The human body needs time to make specific antibodies to fight dengue. Tests are most accurate when they are done three days or more after symptoms begin. Patients should be tested for dengue Immunoglobulin M (IgM) — produced by the body in response to an infection — only after three to six days after the onset of symptoms. If the patient is tested beyond the eighth day and if the reports show the presence of IgG (Immunoglobulin G), that means the person had a prior infection,” Dr. Ravi explained.

“However, some patients are testing negative in spite of maintaining the right timing of testing. This is possible if the patient has been exposed to the dengue virus earlier and has developed a secondary infection. In such cases, the response is blunted because the immune system has already seen the virus,” he said.

Mohammed Sharief, State Programme Officer, National Vector Borne Disease Control Programme (NVBDCP), said a MAC-ELISA (Membrane attack complex – enzyme-linked immunoassay) is the standard test for detection of IgM and IgG antibodies as a rapid antigen test is not always accurate.

Asserting that people should not ignore any fever or related symptoms even if they test negative, Dr. Sharief said, “The response to an infection is not the same in every individual. There is no need for panic as the dengue surge is likely to stabilise by mid-August.”