It is shaping up to be a significant flu season in San Diego County, with the latest weekly respiratory illness report  documenting a local upswing in cases and patient volume that intensified in the final half of December and continues to occupy the health care community into the new year. Last week, 13% of local emergency room patients had flulike symptoms, a four percentage-point jump compared to just one week earlier, and five points greater than the level observed during the same week last season, according to the county health department’s report. Make no mistake, this is shaping up to be the fiercest influenza onslaught since the 2022-2023 season, which saw its rapid increase in October, a few months earlier than the flu’s typical winter surge. “Our wastewater activity for (influenza A) is higher than it’s been in the last two years, significantly higher,” said Dr. Seema Shah, San Diego County’s interim deputy public health officer. “We were sort of overdue for a pretty big flu season, and so it’s not entirely surprising that we’re having quite a bit of flu.” And there has been a similar jump in this year’s cases. The county lists 3,567 positive flu tests were reported in the final full week of December, more than a third of the season total tallied since July in a single seven-day span. The trend echoes a nationwide increase in flu activity, with the U.S. Centers for Disease Control and Prevention reporting that 18.7 percent of flu tests performed by clinical laboratories nationwide came back positive. San Diego County is running quite a bit hotter, topping out at 31 percent last week. It is unclear the extent to which San Diego County’s recent surge parallels other parts of the state. The California Department of Public Health suspended its weekly reporting for the final two weeks of December, planning to resume on Jan. 10. The CDC characterizes California’s influenza activity level as “very high,” with even greater levels detected in Oregon, New Mexico, Louisiana, Alabama and Tennessee. Sharp Grossmont Emergency Room on Friday, Jan. 3, 2025 in La Mesa, CA. (Meg McLaughlin / The San Diego Union-Tribune) Urgent care centers and hospital emergency departments are reporting significant increases in the volume of patient visits. Sharp Healthcare, which operates the region’s largest health system, reported a 15 percent increase in emergency department volume since Dec. 26, with its Grossmont and Chula Vista hospitals seeing the largest increases. All told, Sharp reported 140 hospitalizations for those with flu compared to just 19 for those with coronavirus. Scripps Health said wait times have increased in its urgent care centers, though the influx has not yet been large enough to push operations into overflow procedures, which can often see some patients treated in parking lot tents. It was a similar situation at UC San Diego Health, according to Dr. Marlene Millen, the organization’s chief medical information officer of ambulatory care. Holiday scheduling reduces the number of patients arriving for scheduled appointments, but the flu has kept health facilities busy. “The clinics are kind of quieter, but urgent cares and express care and EDs are busy but, so far, they’re not overwhelmed,” Millen said. “I definitely would say that this year feels a little more dramatic because it went from pretty quiet to busy all of a sudden.” Some might wonder, is this the H5N1 bird flu that virologists the world over have been fretting about through the fall? Thus far, Shah said, there are no local signs of H5N1 cases in San Diego County residents. The local public health lab routinely tests flu samples, determining their genetic subtypes, and looking for any that come back unrecognized. Those, she explained, are the ones that could prove to be H5 making an appearance. “That would have raised a lot of alarms, just as it has in other counties where human cases have been detected,” Shah said. “But we have not detected H5-related human cases.” Those who got sick during the holidays might be wondering about the symptoms they experienced and their connection to the current increase in flu activity. While experts say that those getting sick enough to seek medical attention often have fevers, chills and body aches — the classic signs that differentiate the flu from other viral illnesses — many on social media have reported sore throats and persistent runny noses or congestion causing coughs but not necessarily fevers or chills. These, Shah said, are likely flu as well, though what people call the common cold is caused by a wide variety of different viruses. Vaccination, she added, could be a significant factor in determining whether a person ends up experiencing a more cold-like course of illness or a full-blown flu fight. “We won’t know how well the vaccine matched until the end of the season, but that could be a difference in the severity of illness that people are experiencing,” Shah said. That made sense to Millen. “I’ve definitely seen some flu cases this year that are just like more runny nose and sore throat,” Millen said. “I did notice, in a couple of the folks that had the flu and had the milder symptoms, that did get vaccinated.” No statistics were available on the vaccination status of all confirmed flu cases, though even those statistics would be skewed by the fact that mild symptoms are much less likely to ever be confirmed with a test in the first place. So, any breakdown provided by a medical provider is by its very definition an assessment of those who experienced symptoms severe enough to seek medical attention. Scripps Health provided a readout of what has arrived at its broad network of hospitals and clinics. “Among the 2,316 Scripps patients who tested positive for influenza between Dec. 1 and Jan. 1, 697 (30%) were vaccinated through Scripps in 2024,” the provider said in an emailed statement. However, that accounting, the organization cautioned, does not include those who were vaccinated outside the Scripps system, meaning the actual share of vaccinated patients sick enough to seek medical attention was likely higher than 30 percent. So far this season, overall local flu vaccination has been lower than in recent years. The county’s vaccination registry has recorded 905,921 doses administered thus far this season compared to just over 1 million last year and nearly 1.2 million during the 2022-2023 season. Shah noted that vaccines are still available countywide.