Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations

The WHO has recently released a scientific briefing on the modes of transmission of the COVID-19 virus, which can be accessed here.

What does the briefing cover?

The briefing defines the difference between droplets, which are larger than 5 microns and generated by coughing or sneezing, and droplet nuclei, which are less than 5 microns and may be generated during certain medical procedures such as intubation. The briefing also describes the difference between droplet transmission, which requires close contact within 1 m, and airborne transmission of droplet nuclei, which can stay suspended in the air and be transmitted over distances larger than 1 m. Significantly, analysis of a large number of COVID-19 cases in China did not find evidence for airborne transmission. The briefing also provides a summary of the implications of recent studies reporting the detection of COVID-19 virus from air sampling.

Of note, the briefing indicates that there have been no reports of faecal-oral transmission of the COVID-19 virus. Although RNA of the COVID-19 virus has been detected in the stools from COVID-19 patients in multiple studies, there has been only one report claiming the detection of culturable virus from a single stool specimen.

The evidence presented to demonstrate the presence of culturable virus was not comprehensive. The authors did not state how many stool samples were screened that were negative. The conclusion of cell infection was based on the observation by electron microscopy of virus particles on/in Vero cells. However, the authors did not report if there was cytopathic effect or other evidence of cell infection, such as an increase in virus particle number compared with the number in the original stool sample.

Conclusions

Based on their review of available data, the WHO advice regarding transmission modes and disease prevention remain unchanged.

References

https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations

http://weekly.chinacdc.cn/en/article/id/ffa97a96-db2a-4715-9dfb-ef662660e89d

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