The number of COVID-19 patients needing intensive care jumped 20% in the past week, health officials announced in their latest update.

They warned the public that cases of three winter viruses — COVID-19, the flu and respiratory syncytial virus, or RSV — are on the rise. Some cities had hospital staff setting up tents in parking lots to triage patients.

As of Wednesday, there were 346 patients in hospital intensive care units, which is about 13% of available beds. A higher percentage of COVID-19 tests tested positive, 7.6% this week, compared to 6.3% in the report released Thursday.

Statewide, an estimated 11 out of every 100,000 state residents are reported to be affected by the respiratory disease, which has claimed the lives of millions worldwide in the past 2.5 years. Last week, nine out of every 100,000 had COVID.

The official government figures do not take into account the many people who test themselves at home.

Analysis of wastewater from Stanford University in Sacramento and San Jose shows a sharp increase in the causative agent of COVID-19 compared to samples collected two weeks ago. In Davis, samples showed more than double the level of COVID-19 two weeks ago, although the presence of the pathogen was declining.

Influenza A was found in sewage samples at more than twice the level of two weeks ago in Sacramento, Silicon Valley, Gilroy and Southeast San Francisco. RSV levels continued to rise in Sacramento and Palo Alto, but remained stable or declining.

An average of about 12 people a day are dying from COVID-19 in California, health officials said in a report Wednesday. They say that vaccination is the best way to prevent serious illness, hospitalization and death. Unvaccinated people are three times more likely to die from COVID-19 than people who have had at least the first two vaccinations.

Flu vaccines are also available. This there is no vaccine for RSVa disease which can cause serious breathing problems for a baby. Dr. Erica Penn, a California epidemiologist and pediatrician, said parents should consult a doctor if their children show signs of distress, including dilated nostrils, grunting or wheezing, or a full tightening of the diaphragm to suck in air.

The problem with babies in particular, doctors say, is that they haven’t yet developed the reflex to initiate mouth breathing when their noses are too stuffy to get air.