A small coronavirus outbreak at a bathhouse in China suggests that SARS-CoV-2, the virus responsible for the respiratory disease, could still spread and cause infection in warmer, humid environments, providing a potential “epidemiological clue” for the novel coronavirus.

“Previous studies have demonstrated that the transmission rate of a virus is significantly weakened in an environment with high temperature and humidity. However, judging from the results of this study, the transmissibility of SARS-CoV-2 showed no signs of weakening in warm and humid conditions,” writes the research team in JAMA.

SARS-Cov-2 is closely related to severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), although it is known to have a higher transmission rate than other coronaviruses. It is spread through respiratory droplets and physical contact and generally sees an incubation period between three and seven days, though infected individuals may be asymptomatic for up to two weeks. Previous studies have indicated that similar viruses may be impacted by heat and humidity, though experts warn that it is too early to determine how higher temperatures might impact SARS-CoV-2.

“Generally, coronaviruses survive for shorter periods of time at higher temperatures and higher humidity than in cooler or dryer environments. However, we don’t have direct data for this virus, nor do we have direct data for a temperature-based cut-off for inactivation at this point,” according to the Centers for Disease Control and Prevention.

To determine whether heat may impact SARS-CoV-2, scientists in China followed nine men between the ages of 24 and 50 who became infected with the respiratory illness after visiting a bathhouse.

Eight individuals who visited or worked at a bathhouse in Huai’an, about 435 miles northeast of Wuhan, became infected by COVID-19 just days after a man with the disease visited the center. The 300-square-meter (3,200 square feet) center features a swimming pool, showers, and sauna that are shared communally among users. Areas within the facility see temperatures ranging from 25-41°C (69.8-105.8°F) with about 60 percent humidity.

Scientists collected throat swab samples during the men’s hospital stay between January 25 and February 10 that confirmed infection.

Hospital data revealed that the initially infected man had traveled to Wuhan before visiting the bath center on January 18. He developed a fever the following day and was diagnosed with COVID-19 within a week. Seven other patients also showered, used the sauna, and swam in the same area on January 18 and began exhibiting symptoms such as fever, cough, headache, and chest congestion between six and nine days after their visit. The ninth person was an employee of the bathhouse and experienced an onset of the disease on January 30 – 11 days after the initial patient had visited the bathhouse.

However, it is important to note that the findings are presented in a case study, which is not the same as peer-reviewed research. A variety of limitations are associated with case studies because they are mostly based on observational data and can be difficult to replicate, nor do the findings necessarily apply to wider populations.