The Beijing Health Inspection Office launched investigations into five hotels on Tuesday and all five-star hotels across the city will face scrutiny this week, according to Beijing News.

The five hotels are W Hotel Beijing, InterContinental Beijing Sanlitun, Hilton Beijing, Beijing JW Marriott Hotel & Resorts and Shangri-La Hotel Beijing.

Lanmei Test, an independent reviewer, released a video on its official WeChat account on Monday, showing that stamps — only visible under ultraviolet light — left by its employees on hotel sheets, toilets and cups the previous day were still there when they checked in the next day.

The video went viral and raised public concern over the cleanliness of hotels in the city.

In 2011, the Ministry of Health passed a regulation on the administration of public spaces, which requires hotels to change bedclothes for every guest. For long-term guests, bedclothes should be changed at least once a week. Star rated hotels have stricter regulations.

Li Lei contributed to this story.