Whether people infected with new coronary pneumonia can be contagious during the asymptomatic incubation period and when it can be transmitted to others is a major focus of the outbreak. New research shows that new coronavirus infections are highly transmitted during the incubation period, especially during the last three days of the incubation period. The latent period can infect close contacts with characteristics that can lead to isolation gaps and require further strong measures to contain the outbreak.
The above conclusions come from a paper (without peer review) published on March 6 thin by a research team from the School of Public Health of Tongji School of Medicine of Huazhong University of Science and Technology and the School of Medicine of Tongji Medical College of Huazhong University of Science and Technology on March 6 ( without peer review ) by Xu Shunqing, vice president of the School of Public Health of Huazhong University of Science and Technology.
The study assessed the spread potential of 50 infection clusters, including 124 patients, during the incubation period by collecting data such as demographic characteristics, history of exposure and symptom timing of confirmed cases. All secondary cases have been in contact with the first generation of cases prior to the onset of symptoms.
The study estimated that the average incubation period for new coronary pneumonia was 4.9 days (95 percent confidence interval, 4.4 to 5.4 days) and ranged from 0.8 to 11.1 days (2.5 to 97.5%).
The infection curve shows that 73.0% of secondary cases of infection are dated before the onset of symptoms in the first generation of cases, especially during the last three days of the incubation period for the first generation of cases.
Samples showed that 66.2% of secondary cases had been infected within three days of the first generation of cases before symptoms became symptoms
The rapid increase in cases in Wuhan has prompted concerns about the presence of undetected or isolated cases of infection.
People infected with SARS and MERS rarely infect others during the incubation period, but those with new coronavirus infections are different. Whether or not it is infectious and when to infect others is a question worth studying during the incubation period of new coronavirus infection. Most new coronavirus infections without symptoms during the incubation period are of greater concern than a relatively small number of asymptomatic cases, as they can lead to a large number of infections.
In China, all people in close contact with new cases of corolla must be isolated. However, due to limited resources, Wuhan only isolated people who were in close contact with the confirmed patient’s symptoms after the onset, and did not isolate other people who had been in close contact with them before the onset of symptoms. If a person with a new coronavirus infection can spread asymptomaticly during the incubation period, this isolation loophole can lead to a large number of infections.
In the study, the team focused on examining whether and when new coronavirus infections were infected during the incubation period, in order to provide clues to containment measures to reduce the spread of the disease.
Accurately estimating the incubation period of neo-coronary pneumonia is critical to ascertain ingressing whether the incubation period is a potential source of infection. The exposure time of most cases in Wuhan is not clear and therefore cannot be used to estimate the incubation period. Cases of new coronavirus infection are confirmed after a short visit to Wuhan or after a short history of exposure to confirmed cases, and the incubation period can be accurately estimated based on their exact exposure time.
In addition, identifying people in families or communities who have been in contact with confirmed cases of new coronary pneumonia prior to the onset of symptoms can help assess potential routes of transmission during the incubation period. The team collected data from local governments on new coronary pneumonia patients diagnosed outside Wuhan and Hubei provinces. This information includes demographic characteristics, history of exposure or exposure, time of exposure and when symptoms occur, and the relationship between cluster-confirmed cases.
In order to improve the accuracy of the incubation period estimates, the team selected cases limited to cases with an accurate exposure period of no more than three days. In addition, the researchers only selected cases of symptoms before the Spring Festival (January 25, 2020) to reduce the deviation of contact time, because the Spring Festival visiting friends and relatives of the custom may lead to increased contact and communication, and thus contact with unknown sources of infection.
Therefore, the researchers collected cases with an estimated incubation period that met the following criteria:
1, travel to Wuhan short or with the confirmed case has a history of contact, but did not contact other potential sources of infection;
2. Their stay or exposure time is not more than three days, and they can obtain specific information about the date of exposure and the onset of symptoms.
After meeting the above conditions, a total of 106 cases were included for incubation period analysis. The team used data on new coronary pneumonia cases in households or communities as of February 16, 2020 to assess the potential for transmission during the asymptomatic incubation period.
The team defined the first generation of cases in the cluster as people who had been to Wuhan or had a history of exposure (contact with people from Wuhan, or confirmed cases) and were confirmed as positive for the new coronavirus. Secondary cases are defined as having a clear history of exposure to first-generation cases and have been identified as new coronaviruses, but there are no other potential sources of infection.
Cases in clusters are consistent with the following conditions: secondary cases and first-generation cases have a history of close contact prior to the onset of symptoms, and the first-generation and secondary cases have complete information on the time of exposure and when symptoms occur. A total of 50 first-generation cases and 74 secondary cases in 50 clusters were included for analysis.
Of the 106 confirmed cases of new coronary pneumonia, there was a clear history of travel or exposure, with a median age of 41 years (19-73 years), of which 70 (66.0%) were male.
The majority (82.1%) had a 1-2 day exposure period, while 67.9% had a short travel history of travel to Wuhan. The researchers estimated an average incubation period of 4.9 days (95 percent confidence range of 4.4 to 5.4 days) and a range of 0.8 to 11.1 days (2.5 to 97.5%).
Of the 50 clusters infected with the new coronavirus, the median age of the first generation of cases was 47 years (range 21 to 73 years), of which 58.0% were men, with a history of going to Wuhan.
The median age of 74 secondary cases was 45 years (range 7-83) and 45.9% for men. As shown in figure 2, the majority of secondary cases (89.2 per cent) develop symptoms after their first-generation cases, but there are four secondary cases (5.4 per cent; in groups 5, 21, 29 and 46) the symptoms occur before the first generation of cases. There were four first-generation and secondary cases (5.4 per cent; in groups 22, 35, 41 and 43) with symptoms on the same day. The average and standard deviation (SD) of the observed sequence interval sat was 4.1 to 3.3 days, with 2.5 and 97.5 percentiles, respectively, at -1 and 13 days.
After the symptom episode date set in the first generation case, the peak of the infection curve in the second generation case is shown before the outbreak date of the symptoms in the first generation case.
The majority of secondary cases (73.0%) were infected prior to the onset of symptoms in the first generation of cases, while 18.9% and 8.1% were infected on the day and after the onset of symptoms in the first generation of cases.
It is worth noting that 66.2% of secondary cases were infected within three days of the first generation of cases before the onset of symptoms.
Recommendation: Once diagnosed, all close contacts must be traced back to at least three days prior to the onset of the case, all isolated
The study has shown preliminary evidence that new coronavirus infections are contagious during asymptomatic periods. By estimating the incubation period using an accurate history of exposure to confirmed cases, the researchers found that the incubation period, especially in the last three days of the incubation period, was contagion. In these clusters, they found four secondary cases with symptoms earlier than the first generation, further providing evidence of latent transmission. The findings could help governments take strong and effective measures to curb the spread of the new coronavirus and predict epidemic trends.
The researchers’ analysis of the infection curve in cluster relay cases found that people with new coronavirus infections may infect others before the onset of the disease. The findings also suggest that close contacts in patients with new coronary pneumonia should also be acutely isolated three days before the onset of symptoms. The results suggest that current isolation measures are flawed and may lead to some asymptomatic cases of incubation not being isolated in a timely manner and becoming a potential source of infection.
At present, China has mandatory isolation of close contacts of all confirmed cases, but only requires the isolation of close contacts after a symptomatic attack or virus-positive test, which does not include close contacts before the onset of symptoms or virus positive testing, the paper said. Current isolation measures are not sufficient to curb the spread of the virus, especially for individuals and their families who are isolated together at home if the asymptomatic in their incubation period has the potential to spread the virus.
Once a confirmed case is available, the researchers recommend that all close contacts must be traced back to at least three days before the onset of the case’s symptoms, and then isolated. If the patient engages in extensive social activity before the onset of symptoms, the risk of transmission increases significantly. As a result, restrictions on social activities and travel to and from cities in severely affected areas may be effective in reducing transmission.
Still, the study has some limitations. For those without symptoms, there is no data on virus detection during the incubation period. Since most close contacts in China are not able to perform viral nucleic acid assays, it is difficult to obtain evidence of molecular biological monitoring in a short period of time. The authors argue that if a group of close contacts were tested for nucleic acid, more convincing evidence would be provided that patients with neo-coronary pneumonia spread during the incubation period.
(Original title: 124 new crown studies: 60% of secondary cases were infected 3 days before the onset of a generation of cases)
Journalist He Liping