By Moses Charedzera
Lancet Clinical laboratories CEO Dr Charles Muronda has explained the puzzling phenomenon of covid-19 infected individuals who however test negative.
This was after a question was raised by one of the followers on the YAFM webinar held on Friday why one of the survivors who gave his testimony indicated he had tested negative at Lancet Clinical Laboratories despite presenting with the symptoms of the disease.
Dr Muronda said that for a PCR test to record positive there should be enough viral load in the sample and the load may not be detected in the early days of infection.
“There are many factors that are going to determine whether a person is negative or positive. PCR basically detects the presence of the virus in are sample, that is called the viral load.
Let’s say you have contracted covid-19 today, it takes up to three, four, five days for the amount of virus in your cell to be tested to be picked up.
“What I am saying is that day one, day two day three, even day four, if you are tested with PCR you may end up with a negative result. It doesn’t mean that you are negative, but the viral road in the sample is not enough for the machine to detect.
As time moves and we reach day ten the viral load falls, so if you are tested at day fourteen, quite often the test is negative,” he said.
Dr Muronda attributed false negative results to a number of factors including the skill and training of the staff doing the tests, the handling of the sample as well as the quality of the equipment processing the sample.
“False negatives may be recorded because of a number of factors, the first one being viral load may be low and secondly, If the person taking the sample is not well trained.
Collecting a covid-19 sample is a specialised task where you have to put the swab in the nose and make sure it gets to the back of the nose.
“If the person taking the sample is not well trained, he or she can take an inadequate sample. So, if a sample does not reach the back of the nostril it will register a false negative.
Similarly, if the sample is taken from the throat, it has a lower yield of the viral material. After that the sample should be put in special media. If the sample is put in an ordinary tool without the special media it will disintegrate and you will end up getting a negative result, said Dr Muronda
The Lancet boss also noted that proper transportation of the sample is a factor in recording false negatives, adding that laboratories that have not upgraded their equipment can also report a lot of false negatives.