Anti-Covid fight false negatives in Mumbai

MUMBAI: A city doctor who developed a dry cough and fever was recently relieved in the laboratory run by BMC. However, his relief turned to dismay a couple of days later when he tested positive at a private hospital where he went, due to worsening symptoms; he continues in the hospital.

Elsewhere in the city, a 30-year-old man tested negative at a private hospital only to test positive in Kasturba.

they are clearly emerging as an additional challenge in the midst of a furious epidemic. There is a huge false-negative problem, said Dr. Jayanti Shastri, director of the civic-managed Molecular Diagnostic Laboratory at Kasturba Hospital, which is the main testing center.

Studies in Wuhan, the Chinese province where the Covid-19 pandemic began, found that false negative reports could be as high as 30%. A third of all Covid patients could receive a negative result, despite presenting clinical symptoms.

A false negative result means that a patient's test results are negative even though they harbor the virus. Such patients are sent back from hospitals or, worse, have a false sense of relief, lower their guard, and spread the infection at home and within the community.

The experts listed a number of reasons: the nature of the virus, the incubation period of the infection, inadequate sample collection, the types of kits available on the market, etc. “There needs to be an adequate amount of virus in the body for a test to detect it. This is called the detection limit by the team, Dr. Shastri said.

She said the ideal time for the test would be five days after infection when there is an adequate viral load. However, infectious disease specialists like Dr. Tanu Singhal said the test's sensitivity decreases beyond seven days of symptoms.

Mumbai doctors have found another mischievous fact about the new coronavirus: its presence in the patient's body increases and decreases every day, contributing to false negative tests. A patient may test negative today, but it will test positive a few days later, Shastri said, adding that this is why he discharges a patient only after two consecutive tests taken 72 hours apart are negative.

The virus has many public health dilemmas, or it's like a puzzle, Dr. Shastri said.

Wuhan's study looked at two groups of positive patients: severe and mild. He found that the sputum samples showed the highest positivity in both groups: 89.9% in severe and 82.2% in mild. However, nasal swabs had a positivity of 73.3% in severe cases and 72.1% in mild cases, while it was lower for throat swabs (60%, 61.3%, respectively). Doctors here also report similar findings.

Dr. Nilesh Shah of the Metropolis Laboratory said that nasopharyngeal swabs should be taken in the background.

If the collection is not done correctly, it is likely that you will get a negative result even if the patient has the virus, he said.

Dr. Singhal said that the published medical literature showed that nasopharyngeal and oropharyngeal swabs under ideal conditions detect 50-60% of cases. This sensitivity decreases further if the collection method is not adequate or if a sample is not properly transported and processed, added Dr. Singhal.

Additionally, there are several Covid test kits available on the market. Each kit can have a different sensitivity and show different results.

A doctor at a public hospital said they depend heavily on a patient's clinical symptoms. We have seen cases in which patients test negative even though their CT shows a lung affected by the crown, the doctor said.

However, the doctor added a word of warning: “This does not mean that the test is not reliable. It only means that people must follow the 14-day quarantine rule, even if they test negative.