BEIJING (Reuters) – China has found the trading sections for meat and seafood in Beijing’s wholesale food market to be severely contaminated with the new coronavirus and suspects the area’s low temperature and high humidity may have been contributing factors, officials said on Thursday.

Their preliminary report comes as the country’s capital tackles a resurgence of COVID-19 cases over the past week linked to the massive Xinfadi food center, which houses warehouses and trading halls in an area the size of nearly 160 soccer pitches.

The latest outbreak infected more than 100 people and raised fears of wider contagion in China.

Among the patients who work at the Xinfadi market, most serve at seafood and aquatic product stalls, followed by the beef and mutton section, and patients from the seafood market showed symptoms earlier than others, Wu Zunyou, chief epidemiologist at the Chinese Center for Disease Control and Prevention, said at a daily briefing on Thursday.

Low temperatures favorable to viral survival as well as high humidity might be possible explanations for why seafood markets could be a source of outbreaks based on a preliminary assessment, Wu said, cautioning that further investigation was necessary.

China has halted imports from European salmon suppliers this week amid fears they may be linked to the recent outbreak in Beijing.

Health officials have also warned against eating raw salmon after the virus was discovered on chopping boards used for imported salmon, although the origin of the outbreak is not known.

Low standards of hygiene in wholesale food markets and vulnerabilities in its food supply chain need to be urgently addressed, a leading body of the ruling Communist Party said this week.