Influenza activity continues to increase in the United States, and most of the country — including San Joaquin County — is now experiencing influenza-like illness, according to the Centers for Disease Control and Prevention's latest report.
However, local health officials believe the worst is yet to come.
"So far, from what I've heard, California has not been hit as hard as other parts of the country — yet," said Karen Furst, health officer for San Joaquin County.
Still, officials recommend the influenza vaccination for people who have not yet been vaccinated this season, and antiviral treatment as early as possible for people who do get sick and are at high risk of flu complications. To date, two adults under the age of 65 have died from influenza in California.
Nationwide, flu-related child and infant deaths climbed to 18, and outpatient visits for flu symptoms jumped in the last week of 2012.
The CDC's Tom Skinner said people who come down with this flu can be very sick, with severe muscle aches and high-grade fever lasting four or five days.
For children, the elderly and people with underlying health conditions, it can be life-threatening, he said.
As early as December, the CDC was warning that the flu season had gotten off to its quickest start in nearly a decade, a sign that it could be a bad year for the illness.
At that time, Dr. Thomas Frieden, the center's director, urged people to get a flu shot to minimize the impact of the deadly disease's spread.
The good news? So far this season, 91 percent of the influenza viruses that have been analyzed at the CDC are like the viruses included in the 2012-13 influenza vaccine. The match between the vaccine virus and circulating viruses is one factor in how well the vaccine works.
The CDC tracks influenza activity year-round and publishes an online report weekly on Fridays.
According to the most recent available data, as of Dec. 29, 2012, the proportion of people seeing their health care provider for influenza-like illness nationwide has been elevated for four consecutive weeks.
However, at this time, California is among the nine states still reporting low or minimal rates.
The state's rates are regional, not widespread, according to Furst.
"Surveillance systems in place show we're seeing some influenza pockets in San Joaquin County," she said.
For example, hospitalizations for influenza and pneumonia increased 4.7 percent in the second-to-last week of December 2012, and 6.2 percent the last week in Northern California Kaiser Permanente hospitals, compared to 4.2 percent in the third-to-last week, according to the California Department of Health.
The number of actual cases are unavailable since influenza is not a reportable disease under guidelines issued by health officials.
Flu season in the United States typically peaks in February and March — sometimes even as late as April — but this season, a November flu arrival in the Southeast has doctors betting the season will peak earlier on the West Coast.
The end of the holidays, and the return of children to classrooms and adults to work, are expected to jump-start flu season in the state.
In San Joaquin County, the peak is typically in February, although it was late last year, Furst said.
While the timing of influenza seasons is impossible to perfectly predict, based on past experience the CDC said it is likely that flu activity will continue for some time.
One factor that may indicate increased severity this season is the predominant circulating type of influenza virus, which accounts for about 76 percent of the viruses reported. Seasons with this strain have been more severe, with higher numbers of hospitalizations and deaths, according to the CDC.
The Associated Press contributed to this report.
Contact reporter Jennifer Bonnett at email@example.com.