A salesman promoting health products to the elderly and travelled around China has been linked to 102 confirmed COVID-19 infections.

This has prompted tens of millions of people into lockdown.

The man travelled while unknowingly infectious for several days before being tracked down by health authorities as a close contact of a confirmed case.

“The super-spreading phenomenon occurred in our province mainly because when the superspreader was discovered, he was still in the early phase of his infection and had relatively strong ability to shed the virus,” Zhao Qinglong, an official with the Jilin provincial disease control and prevention centre, told state-run news agency Xinhua.

Over a four-day period, the man held marketing sessions and seminars promoting health products that targeted elderly residents, with 79 people who attended the meeting going on to infect 23 close contacts.

All those infected have been quickly placed in quarantine.

These “health clubs” have come under scrutiny since the event as the sessions are unable to be regulated like large gatherings as they are usually held in private homes.

“The infected people were gathered in an enclosed space for a long time,” Zhao told Xinhua.

“Most of them are middle-aged and elderly people with underlying health conditions, and weak immunity, and therefore extremely susceptible to infection.”

The average age of those infected is 63, with the oldest being 87 years of age.

These health clubs are now being investigated by authorities to check whether the sessions violated any regulations.

This article originally appeared on Over60.