Nine US states have reported record increases in Covid-19 cases over the last seven days, mostly in the upper Midwest and West where chilly weather is forcing more activities indoors, Reuters reported.

On Saturday alone, four states — Kentucky, Minnesota, Montana and Wisconsin — saw record increases in new cases and nationally nearly 49,000 new infections were reported, the highest for a Saturday in seven weeks, according to a Reuters analysis. Kansas, Nebraska, New Hampshire, South Dakota and Wyoming also set new records for cases last week.

Daytime highs in many of these states are now in the 50s Fahrenheit (10 Celsius). Health experts have long warned that colder temperatures driving people inside could promote the spread of the virus.