By FENG Yuchen

The market reacted swiftly to news that Zhou Wei, CEO of Winning Healthcare, had been detained by authorities in Maoming on July 1. Its shares plummeted from 10.82 yuan on June 30 to 7.72 yuan on Wednesday.

The company's market value fell by nearly 4.6 billion yuan (US$640 million) on Monday.

According to Chinese law, a "supervision committee" may detain individuals only when they face charges of corruption, bribery, or illegal activities committed while on duty. The work of such committees generally concerns government business.

Winning Healthcare issued a statement that other executives are at their desks as usual. The company says it has not yet received any formal notice regarding the investigation.

An intriguing aspect of the situation is that Winning Healthcare's headquarters are in Shanghai, and most of its operations are conducted there. 

But Zhou was detained in Maoming, a southern city in Guangdong province that is a long way from Shanghai. Speculation suggests that Zhou might be implicated in a case involving one of the company's clients. 

Recent reports indicated that a director of a public hospital in Maoming was also under investigation. 

Winning Healthcare primarily serves domestic public hospitals and healthcare departments. Recent successful bids in Maoming, though nothing unusual in themselves, have fueled speculation about Zhou's detainment.