Covid long: the controversial study

For most patients, symptoms of Covid will last two to three weeks. For others, it can take a lot longer! Some will experience symptoms for months. This concerns both hospitalized and non-hospitalized patients. We then speak of long Covid. However, these symptoms are not specific to Covid and can have many other causes. To see more clearly, some authors wanted to carry out serological tests in patients who think they may have been infected with virus and reporting signs of Covid along. The study was recently published in the JAMA (Journal of the American Medical Association).

Loss of smell, the only symptom of a real long Covid?

No less than 26,823 patients were included in this French study, comprising 51.2% women and 48.8% men. The average age was 49.4 years. The participants received a kit to perform a self-collection of blood at home. On this levy, antibody anti-SARS-CoV-2 were sought: 1,091 patients had a positive serological test.

The patients also received a questionnaire. A first part of the questionnaire asked participants if they thought they had been infected with the virus and if so, if the infection had been confirmed by a test, whatever its nature. Among the 1,091 people with a positive serological test, 453 (41.5%) reported having been infected with Covid-19.

A second part of the questionnaire focused on the symptoms experienced by the patients: sleep, pains muscle, joint pain, headache back, fatigue, trouble concentrating, constipation, stomach pain, headache, difficulty breathing, palpitation, loss of taste and wheresmell, skin problem, hearing problem, cough, dizziness, chest pain. The list of these symptoms has been compiled according to the symptoms of Covid long reported in the scientific literature. According to the authors, there is a statistically significant link between thinking you have had Covid and reporting persistent symptoms. On the other hand, there would not be a significant link between having a positive serology and the fact of declaring persistent symptoms, except for the symptom of loss of smell. That is, this study suggests that thinking you have been infected is more, statistically speaking, related to feeling symptoms months after infection than actually having been infected! The authors wish to emphasize that in no case do they question either the existence of the long Covid, or the symptoms described by the patients. On the other hand, they wish to warn against a too rapid diagnosis of Covid long, the symptoms being not very specific.

A criticized methodology

To find out whether the patient has been infected with the virus or not, this study is based on a serological test. The serological test used displays a sensitivity of 87% and a specificity of 97.5%. If we consider that at the time of the study, about 4% of the French population was infected, this means that we can expect 140 false negatives and 644 false positives. The population presenting a negative serological test is large (n = 25,732) and the number of false negatives does not change the situation. On the other hand, the population presenting a positive serological test is small (n = 1,091) and the number of false positives represents more than half of the population! TO in the light of this analysis, the conclusions of this study therefore lose statistical power.

Moreover, the negativity of a serological test is not an undeniable marker of the absence of contamination. The antibody level can decrease very quickly after infection while symptoms may persist. These results should therefore be taken with a grain of salt!