A case-series investigation of more than 44,000 COVID-19 patients in Tokyo in 2020 reveals that SARS-CoV-2 transmission events in healthcare and nightlife settings (eg, bars and nightclubs) were most likely to involve at least five infections, with nightlife cases more likely to generate further spread.

A team led by researchers at Tohoku University Graduate School of Medicine in Japan analyzed epidemiologic data from 44,054 COVID-19 patients from Jan 23 to Dec 5, 2020, before vaccines were available. The research was published late last week in JAMA Network Open.

The authors noted that while Japan advised people to stay home and avoid unnecessary travel, the country didn't impose mandatory lockdowns. Rather, the government recommended closures of targeted businesses and limiting business hours and alcohol sales.

Death rate highest in healthcare settings

The researchers focused on seven transmission settings: imported, nightlife, dining, workplace, household, healthcare, and other. The team identified the likely setting for 13,122 infections, including 6,768 households, 2,733 healthcare, and 1,174 nightlife cases.

The first cases appeared in nightlife settings, followed by household and healthcare. Of the more than 6,000 transmission settings, nightlife (18.9%) and healthcare (36.2%) were more likely than dining, workplace, household, and other settings to involve five or more cases.

After adjusting for transmission setting, sex, age group, symptom status, and pandemic wave, the authors found that household and healthcare infections were less likely than nightlife cases to generate further spread (household adjusted odds ratio [aOR], 0.03; healthcare aOR, 0.57).

Of the 30,932 infected patients with unidentified transmission settings, those who had visited nightlife establishments were more likely than others to spread the virus to nonhousehold settings (aOR, 5.30).

The case-fatality rate was highest in healthcare settings (9.8%), with all deaths occurring among patients and visitors. Other risk factors for death were male sex (aOR, 1.90) and age 65 years or older (aOR, 39.85).

"Surveillance and interventions targeting nightlife settings should be prioritized to disrupt COVID-19 transmission, especially in the early stage of an epidemic," the researchers wrote.

• The US Department of Energy (DOE) has concluded that the source of SARS-CoV-2 was probably a lab leak in China, made with what it says is "low confidence" but based on new undisclosed intelligence, according to the Wall Street Journal. The DOE had earlier said it was undecided on the source of the virus. The DOE has shared its findings with other US intelligence agencies, and they have not changed their assessments, according to the New York Times. Four have said, also with low confidence, that a natural source is likely. The Federal Bureau of Investigation, however, has said with moderate confidence that an accidental lab leak is the likely source.
• A doctor's group known for encouraging the use of the antiparasitic drug ivermectin for preventing and treating COVID-19 is now promoting the drug for treating respiratory syncytial virus (RSV) and influenza, the Washington Post reported. The push for treatment of other respiratory viruses comes in the wake of several studies, including one last week that looked at higher dosages and longer duration, that have shown that ivermectin has no benefit for treating COVID. The Front Line COVID-19 Critical Care Alliance has published a protocol for treating RSV and flu with the drug, despite lack of clinical evidence, and it is recommending provider and pharmacy networks to provide virtual visits and prescriptions that patients pay for out of pocket.

The World Health Organization (WHO) on Feb 25 shared the latest investigation details about a Marburg virus outbreak in Equatorial Guinea—the country's first—that officials announced earlier this month.

The investigation was triggered after at least eight deaths occurred between Jan 7 and Feb 7 in people from two villages in the same district who experienced hemorrhagic fever. Blood samples collected from eight of their contacts were negative for Ebola and Marburg viruses. Of samples collected for eight additional contacts, one was positive for Marburg, from a patient who died on Feb 10 at a district hospital.

The patient was a contact of four of the people who had died earlier from similar symptoms.

So far, the outbreak total remains at nine cases, including the confirmed case, four probable cases, and four classified as suspected. All cases were fatal. The patient with the lab-confirmed infection was the only one who died in a hospital—the rest died in community settings, a factor known to pose a high risk of further disease spread.

The WHO said all nine patients had contact with a relative who had similar symptoms or had participated in a burial of a patient with similar symptoms, another practice known to enhance the transmission risk.

The WHO said the risk to Equatorial Guinea is high, and it put the risk to the region as medium. The risk is low at the global level.

Marburg virus, a close relative of Ebola, spreads through contact with infected body fluids of infected people. It has a case-fatality rate as high as 88%, and so far there are no approved vaccines or specific treatments.