The number of flu-related deaths this season in Maine has reached 21, according to the Maine Center for Disease Control and Prevention.

Emily Spencer, a spokeswoman for the state agency, said the number includes people who have died from complications from flu.

“This is likely an underrepresentation because many individuals die of secondary infections that are attributable to influenza, but influenza might not be listed on the death certificate,” said Sara Robinson, an epidemiologist with the Maine CDC.

The number of deaths nearly doubled in the past week. There were 13 deaths at least partly attributable to influenza in Maine through Jan. 11, according to the Maine CDC. Maine reported 1,187 cases of people testing positive for flu through Jan. 13, and 391 of those cases were recorded in the latest seven-day period.

Spencer could not immediately provide comparison data to previous flu seasons in Maine as of Jan. 19, and cautioned that flu seasons do not begin and end at the same time. There were 71 deaths in Maine during the 2016-17 flu season, which started and ended later than usual.

Almost all of the cases this season in Maine have been H3N2, a virulent strain of influenza A that is more likely to result in hospitalization. By the end of last week, 327 flu cases in Maine required hospitalization, or about 28 percent of the positive flu tests reported to the state.

“This particular strain tends to affect older adults, which naturally leads to more hospitalizations and more deaths than a strain that affects a younger population,” Robinson said.

The spike in the number of flu cases has led to growing precautions around the state, including by churches that are suspending hand-touching and other traditional rituals that might spread the virus.

Across the nation, the U.S. Centers for Disease Control and Prevention reported 74,562 confirmed cases of the flu through testing, although actual numbers of people who fall ill from influenza are much higher, as many recover at home and are not tested for the flu. All states except Hawaii were reporting widespread flu activity in the latest U.S. CDC report, which measured flu activity through Jan. 13. Alabama’s governor issued a state emergency caused by flu outbreaks on Jan. 11, and other southern states, such as Florida and Georgia, are reporting that flu outbreaks are taxing hospital emergency departments, according to news reports.

Staff Writer Joe Lawlor contributed to this report.