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Many times during this Covid-19 madness we have helped answer questions from the audience. You often get one and think, ‘That will be easy.’ Then sometimes you get one that is anything but easy to answer.
Photo: AFP
More than two weeks ago, a member of the RNZ audience contacted the first question below, asking if we could raise it with the Ministry of Health.
What follows are the follow-up questions over the course of 12 days.
Do you have information on the percentage of false negatives that can occur with the Covid-19 test being performed in New Zealand; that is, of the numbers of tests that turn out negative, which number is really wrong (shows a negative result when, in fact, the person is positive for Covid-19)?
“The detection of SARS-CoV-2 varies mainly according to the stage of the disease and the anatomical site examined. The vast majority of people evaluated are those with mild symptoms in the community. We do not have a gold standard to compare the results with We are not performing invasive samples, CT scans, etc., so they cannot give a precise sensitivity for use in community public health interventions, although the reduction in new cases and trends in positivity rates speaks of their usefulness. in this environment. “
I think I need to rephrase it (the original question) a little bit. The direct question I think remains: have there been false negatives? If so, how many as a percentage of tests?
“These are not data we have centrally. Doctors acknowledge that detection is more difficult in the upper respiratory tract, and to mitigate this, patients who test negative will either receive more tests or be treated as probable cases based on their other research.”
“An example is seen in Case 1 where the patient was admitted and examined. Two previous tests were negative for Covid-19. An additional test with a more specific sample was positive as seen here:
Unique case of Covid-19 confirmed in New Zealand | NZ Ministry of Health]
The first case of COVID-19 is now confirmed in New Zealand in a 60-year-old who recently returned from Iran. The test results were formally reported to the [www.health.govt.nz Ministry at around 4.15pm this afternoon]”
The previous answer says that the information is not kept centrally. Where does it take place? Is anyone compiling and parsing? Is it an important part of the general data given the damage that can be caused by one or two undetected cases in the community? Are there other known cases, in addition to the previous reference, in which people have turned out negative only to be confirmed later? If so, do we know how many and if they have been part of any cluster activity?
“Public health units and hospitals will save the information; they are likely to collect, learn from experience and new literature; however, we cannot give details on each area. Peer-reviewed journal articles tend to be written when there is More information is available on the subject.
“The interpretation of a SARS-CoV-2 (Covid-19) laboratory result should be considered within the general context of the patient, such as the time elapsed since the last contact with a probable or confirmed case, presenting symptoms, duration of symptoms , type and quality of the sample, and a time sample was collected in relation to the onset of symptoms in the person A negative test at the beginning of exposure to a confirmed case does not prevent someone from developing symptoms and having a positive test later in the fourteen days since the last exposure to the case, and it would not be seen as a false negative. For these reasons, we cannot report the number of false negatives. “
* See all Covid-19 RNZ coverage
I suppose the general question remains: is the Ministry satisfied with the effectiveness of the tests?
“Regarding the effectiveness of the tests, yes, the Ministry is happy, but we also continue to review available evidence, products and processes to see any further improvement and modification that we can make.”
“I asked one of our labs to respond more regarding improvements etc. and I will talk about that again.”
That would be great in the labs. The previous responses tended to suggest that the Ministry had no evidence, so any clues as to what those reviews have found / are finding, etc.?
“We believe that PCR tests are suitable for diagnosing diseases both in the hospital and in the community, but we recognize that, as with all tests, they have their limitations. These limitations are primarily that it is difficult to detect the disease late in the infection, and that the readily available places in the body to test, the nasopharynx and throat, are not where the virus replicates as the infection sets in.
“The way that labs and public health overcome these limitations is by using inpatient sputum specimens where nasopharyngeal or throat specimens are negative, but a high suspicion of illness persists, and from a health perspective public, highly suspicious cases (based on clinical and epidemiological reasons) with negative evidence a probable case. “
Does your head hurt? Mine does. To summarize, I have not yet been able to deduce whether false negatives have been a problem. Or, in fact, if they are being tracked properly.
- if you have symptoms for coronavirus, call the NZ Covid-19 health line at 0800 358 5453 (+64 9358 5453 for international SIMs) or call your GP
