False Negative queer anti-Covid fight
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A city doctor who developed dry cough and fever was relieved to test negative for Covid-19 at the BMC-run Kasturba Hospital laboratory recently. His relief, though, turned into dismay a couple of days later when he tested positive at a private hospital he drove himself to, due to worsening of his symptoms; he continues in hospital.

False-negative reports are clearly emerging as an additional challenge amid a raging epidemic. “There is a big problem of false negatives,” said Dr. Jayanti Shastri, head of civic-run Kasturba Hospital’s Molecular Diagnostic Laboratory, which is the main testing center.

What's a false-negative result?

Patient’s test results are “negative” even though he harbors the virus. Such patients get sent back or, worse, they get a false sense of relief, drop their guard, and spread the infection at home and within the community.

#Experts listed a series of reasons as follows:

- Nature of the virus, the incubation period of the infection, improper collection of samples, types of kits available in the market and so on.

- There needs to be an adequate amount of viruses in the body for a test to detect it. This is called the limit of detection by equipment. Ideal time to test would be five days into the infection when there is adequate viral load.

- Test’s sensitivity drops beyond seven days of symptoms. Patients (especially those without symptoms) have no foolproof way of knowing if they are in their fifth or seventh day of infection.

- Another “mischievous” fact about the novel coronavirus—its presence in the patient’s body waxes and wanes every day, contributing to the false-negative tests. A patient may test negative today but will test positive a few days later.

- Dr Nilesh Shah of Metropolis Laboratory said nasopharyngeal swabs have to be taken “deep inside”. “If the collection isn’t done properly, you are likely to get a negative even if the patient has the virus,” he said.

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

- There are several Covid testing kits available in the market. Each kit may have different sensitivity and different results.

#Wuhan Studies :

The Chinese province found false-negative reports could be as high as 30%. A third of all Covid patients could thus receive a negative result—despite exhibiting clinical symptoms. The Wuhan study looked at two groups of positive patients—severe and mild. It found sputum samples showed the highest positivity in both groups: 89.9% in severe and 82.2% in mild. Nasal swabs, though, had a positivity of 73.3% in severe cases and 72.1% in mild ones while it was further down for throat swabs (60%, 61.3%, respectively). Doctors here too report similar findings.

The doctor, though, added a word of caution: “This doesn't mean the test is unreliable. It only means people should follow the 14-day quarantine rule even if they test negative.”

Source: https://health.economictimes.indiatimes.com/news/industry/false-negatives-queer-anti-covid-fight-in-mumbai/75076349
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