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HKUMed

Tracking Transmission

The rapid transmission dynamics of the disease have been a focus of our work from the outset. Since publishing early findings in January on the spread of the disease, described on page 10, we have continued to deepen knowledge about the infectiousness of SARS-CoV-2 and how it might be controlled.

Over the past 15 years, researchers in the School of Public Health have developed methods for culturing human tissues in the laboratory and applying them to study a range of respiratory viruses, such as avian flu H5N1, H5N6, H7N9, H1N1 and MERS-CoV, as well as SARS-CoV-2.
  • Some patients infected with COVID-19 were shown to be shedding the virus 2–3 days before the first symptoms appear — an early and important finding concerning infectiveness.
  • The eyes were singled out as an important route of infection after a study showed SARS-CoV-2 can infect human airways and eyes more efficiently than SARS. SARS-CoV-2 was also detected in the conjunctival secretions of patients without ocular symptoms, suggesting this is a possible route of transmission.
The SARS-CoV-2 virus was shown to infect human airways and eyes more efficiently than SARS-CoV, implying that the eyes may be an important route of SARS-CoV-2 infection.
  • Prolonged survival of the virus on smooth surfaces highlighted that the virus may be transmitted indirectly via contaminated fomites and hands.
  • Shedding of the infectious virus was shown to occur for at least 9–10 days after the onset of symptoms, a finding that led the Hong Kong Hospital Authority and WHO to amend their policy on discharging patients from
    hospital isolation.
  • The prevalence of the disease in the population has been the subject of several studies. One study found 3.8 per cent of Hong Kong residents returning from Hubei in February/March 2020 were asymptomatic carriers of the virus. Another estimated that the early spread of the pandemic in Wuhan and Seattle was far more extensive than initially reported, based on a comparison between influenza cases and confirmed COVID-19 cases.
  • Asymptomatic cases were also found among passengers quarantined on a cruise ship, based on seroprevalence and virus shedding there, adding more evidence to the challenge of infection control.
  • In the environment around hospitalised patients with SARS-CoV-2, patients’ phones were found to be the most contaminated with the virus, followed by their bed rails and toilet door handles.
  • A new wave of infections in Hong Kong in summer 2020 was shown to be caused by two unique clusters of SARS-CoV-2 that were both closely related to imported strains. This suggested the outbreak was likely not precipitated by silent carriers from previous waves.
  • Superspreading events, in which a few infected patients infect many people, were identified in a study of 1,038 SARS-CoV-2 cases who were confirmed between January 23 and April 28. HKUMed researchers estimated 19 per cent of the cases seeded 80 per cent of local transmission.
“Superspreading” was shown to be a feature of COVID-19 in a study that used contact tracing data to identify all clusters of COVID-19 in Hong Kong from January 23 to April 28.
  • Proof of in-flight transmission aboard aircraft was provided in September when an international team of researchers, including HKUMed, showed that four patients confirmed with the virus after a 15-hour flight had identical viral genomes and were not all likely to have encountered each other before the flight.

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HKUMed

HKUMed

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HKU Medicine — Committed to advancing research, learning and teaching medicine and health, for the betterment of humanity.