How do double negatives work in Chinese

Coronavirus: Why Do Recovered Patients Test Positive?

An approximately 40-year-old woman in Japan tested positive for SARS-CoV-2 viruses again after her official recovery. She was first diagnosed with the infection on January 29th.

The woman had previously visited the Chinese city of Wuhan, which is considered the starting point of the epidemic, as a tour guide for a tourist group. Although she was still coughing, the woman tested negative on February 6 and was subsequently discharged as cured, a week later she was completely symptom-free. On February 21st, she went to see a doctor again because of a sore throat and stomach ache. She tested positive a second time on the 26th and subsequently developed serious symptoms again.

Cases are also known from China in which subsequent tests on actually cured patients again showed positive results. In order to be considered cured, infected people must meet a number of parameters. They must have been free of fever for more than three days and have overcome any respiratory symptoms. In addition, CT images of the lungs must show a noticeable improvement. In order to ultimately have security, the patients are tested for the virus with further PCR tests. These must be negative on two consecutive days.

Four Chinese patients met all of these requirements and remained in quarantine for another five days. They continued to be tested. However, within five to thirteen days of their official recovery, they were again found to have the dangerous viruses. Tests from various manufacturers all worked. Chinese doctors from Wuhan Hospital announced this in the journal "JAMA".

Multi-phase course?

A troubling explanation for this would be that the disease may have two or more phases. This is well known in other diseases caused by viruses such as measles.

This is contradicted by the fact that the four Chinese tested, in contrast to the Japanese patient, did not develop any symptoms at the time of the second test. However, they did not belong to the extreme cases of their original illness either. Two showed only moderate symptoms, one remained completely asymptomatic.

Measurement errors and inaccuracies? German experts consider the scientific basis of the paper to be questionable.

However, experts are cautiously giving the all-clear. Prof. Dr. Christian Drosten, director of the Institute for Virology at the Berlin Charité, makes it clear that he is not at all convinced of the Chinese findings: "The only thing that is relevant here is the PCR detection. However, this can be done after the first week of symptoms Patients fluctuate: sometimes positive, sometimes negative, while the lungs are still full of the virus, regardless of the symptoms. " The scientific basis of the paper is questionable.

Measurement errors and inaccuracies

There is a second and more likely explanation for the meanwhile negative samples. Errors may have been made during the extraction or the test itself. One must "be very careful about interpreting such positive tests in recovered patients as a reinfection," says Prof. Dr. Isabella Eckerle, head of the emerging viruses research group at Geneva University Hospital. Such findings are also known for other viruses that cause respiratory diseases, such as flu viruses.

On the one hand, the tests used are extremely sensitive. Since virus genetic material can still be present in test subjects who have already recovered, the tests can also work on samples that are no longer infectious. However, there is no indication of the amount in that JAMA report. It is not possible to determine from the outside "whether it is only remnants of the virus or whether there is still an active infection."

Negative PCR tests on consecutive days are a reliable indicator

On the other hand, test results can also be falsified if the sample is taken incorrectly. A swab in the nasopharynx could be very uncomfortable for the patient, and accordingly untrained staff could proceed too hesitantly. As a result, tests could be temporarily negative, according to Eckerle: "If the smear is carried out correctly again, it will detect the virus the next time".

Don't panic because of individual cases

To date, it has been assumed that recovered patients are temporarily immune to SARS-CoV-2 due to the formation of antibodies. This can be concluded from the first reports, according to Florian Krammer, professor of vaccinology at the Icahn School of Medicine in New York, even if the protection would be "not for life, as with some other viruses, but for some time".

The case of the Japanese woman is interesting and patients who have recovered should generally be followed up in order to get an idea of ​​the long-term effects of COVID-19. Nevertheless, one can still assume that a patient has recovered if the PCR tests are negative for a few days, according to Prof. Dr. Krammer.

Due to the few and in some cases poorly documented exceptions to the cases in Japan and China, the experts therefore consider it inappropriate to reconsider the previous conclusions.

  • Coronavirus: quarantine in northern Italy

    The driveways are tight

    A total of 52,000 residents were isolated in eleven cities and towns in northern Italy. Anyone who wants to get in or out of the cordoned off areas needs a special permit. These forces are on the outskirts of Castiglione D'Adda. Anyone who tries to bypass the lock faces "criminal prosecution".

  • Coronavirus: quarantine in northern Italy

    Deserted streets

    All the pubs and shops in the center of Codogno, a city of 15,000, are closed, and only a few people go out. It is still unclear who brought the virus to northern Italy. According to Italy's Prime Minister Giuseppe Conte, the quarantine will initially last for two weeks. This corresponds to the assumed incubation time for the lung disease COVID-19, which is triggered by the pathogen.

  • Coronavirus: quarantine in northern Italy

    Rapid development

    As of Wednesday, only three infections were known across Italy. On Thursday, the virus was detected in a seriously ill 38-year-old in a clinic in Codogno, and then in more and more people around him. His parents were also under observation (photo). However, this man is not "patient zero". More than 130 infected people were counted in the region on Sunday, three died.

  • Coronavirus: quarantine in northern Italy

    Quarantined hamster purchases

    Queuing in front of a supermarket in the cordoned off town of Casalpusterlengo. Customers are only admitted in groups of 40 people. "Everyone has a turn, we just want to avoid chaos and ensure adequate protection," tried to reassure a supermarket employee. Not all customers understand this.

  • Coronavirus: quarantine in northern Italy

    All gone

    Fear of infection with the corona virus is also growing in the nearby cities in northern Italy. Disinfection gel and face masks are sold out in this pharmacy in Turin, as the sign at the entrance reveals. Thin masks such as those used in operating theaters offer only limited protection against viruses and have to be changed regularly.

  • Coronavirus: quarantine in northern Italy

    Double masked

    The disappointment of these masked people can be read in their eyes: The famous Venice Carnival is canceled, so even the additional face mask is of no use. The festival has a centuries-old tradition and is a tourist magnet. The opulent costumes and imaginative masks are internationally known. Normally Venice would have celebrated Carnival until Tuesday.

  • Coronavirus: quarantine in northern Italy

    Catwalk despite Corona

    Milan is only 60 kilometers from the badly affected Codogno. The famous fashion week has been running here since Tuesday. In view of the spread of the corona virus, the fashion house Giorgio Armani presented the latest models in an empty theater hall, the show was broadcast on the Internet. Face masks were available for employees. Other fashion shows took place as planned.

  • Coronavirus: quarantine in northern Italy

    Stadium closed

    While the fashion houses could decide for themselves about their shows, all sporting events in the regions of Lombardy and Veneto were canceled until at least March 1st. With this, the Italian authorities want to curb even further spread of the virus. The first division soccer game Inter Milan against Sampdoria Genoa is also affected.

    Author: Uta Steinwehr