Wastewater Surveillance Shows Plateauing in Viral Concentrations

1,682 New Positive Cases and 6 New Deaths Due to COVID-19 in Los Angeles County

With more individuals using over-the-counter (OTC) tests to assess COVID infections, the county COVID case rate, which doesn’t include the results from OTC tests, may underestimate the level of transmission.  Fortunately, Public Health is able to utilize wastewater surveillance to detect significant changes in viral loads or new variants.

Presently, there are four wastewater treatment plants that perform viral surveillance for SARS-CoV-2.

The two largest plants are the Hyperion Water Reclamation Plant and the Joint Water Pollution Control Plant, serving about 7.5 million LA County residents across most of the county.  At the Hyperion Plant, although viral concentrations declined notably in the first half of September, there was a small increase this past week.  The Joint Water Pollution Control Plant reported small decreases throughout September.

The two smaller plants, the Lancaster Water Reclamation Plant that serves Lancaster and Palmdale, and the Tapia Water Reclamation Facility, serving Calabasas and surrounding areas, reported stable concentrations with small increases the past few days.

While the plateauing in viral concentrations in wastewater may signify that viral transmission is no longer decreasing, because most of our other early alert signals indicate low concern, we remain hopeful that transmission is not increasing at this time. However, the plateauing does highlight the need to carefully monitor the other signals to see if there are any additional signs in the next couple of weeks that suggest changes in transmission patterns or illness severity.

Overall, the county continues to report improved COVID-19 metrics. The 7-day average case count in the county is 1,297, an 8% decline from one week ago when the 7-day average of 1,397 cases was reported.

Over the past seven days, the average number of daily COVID-positive patients in LA County hospitals was 499, a 17% decline from one week ago when the average number of daily COVID-positive patients per day was 602.

Deaths, which typically lag hospitalizations by several weeks, remained stable at an average of 11 deaths reported each day this past week, nearly the same as an average of 12 daily reported deaths a week ago. The 7-day average test positivity rate remains stable at 4.3% over the past week.

The Omicron variant continues to account for 100% of Los Angeles County sequenced specimens, and the BA.5 subvariant of Omicron, remains the predominant subvariant. In the week ending Sept 10, 93% of all sequenced specimens were BA.5, the same as the week before, and the week before that. In Region 9, which includes California, Arizona, Nevada, Hawaii, and all of the U.S. territory in the Pacific Ocean, the BA.5 subvariant is estimated to account for about 91% of sequenced specimens for the week ending September 24. Across the country, as of the week ending September 24, the Centers for Disease Control and Prevention estimates that the BA.5 subvariant accounted for 83% of specimens. And according to the World Health Organization, BA.5 and BA.4 (and their sublineages, including BA.4.6) are the dominant variants in Europe.

The relative proportions of other key sublineages Public Health are tracking in the county have changed only slightly, including BA.2.12.1, which was under 1% last week has now declined all the way to zero. BA 4.6 continues to hover at about 3%. To date, 30 specimens of BA.2.75 total have been detected, with under 1% of sequenced specimens testing positive for this sublineage in the most recently available data.

Also last week, Public Health began tracking a new subvariant, called BF.7, a sublineage of BA.5, and is also referred to as BA.  So far, seven sequenced specimens in LA County have been determined to be from BF.7. One was collected the week of August 6, four were collected the week of August 20, and two were collected the week of September 10.

“I send my deepest sympathies and wishes of peace and comfort to the many families who have lost a loved one from COVID-19,” said Barbara Ferrer, PhD, MPH, MEd, Director of Public Health. “As we begin to enjoy fall and start planning for gatherings and holidays, we need to prepare for the possibility that there can be significant transmission of both influenza and COVID this fall and winter.  Both flu and COVID-19 are likely to infect more people when the days are shorter, and the temperatures are cooler.  This is both because people spend more time indoors where respiratory virus can accumulate and jump more easily from person to person and because cooler weather allows the flu and SARS-CoV-2 virus particles to linger longer in the air and travel further, potentially infecting airways that have lower defenses.  And while we don’t have certainty on what this winter will be like, including how much of a surge in COVID and flu we are likely to have, we do know that as the cooler weather sets in and cases rise, the risks will increase for some people more than others.  Risks are elevated for older residents, for those with underlying health conditions, for those with more exposures, and for those unvaccinated.  As we prepare for the upcoming holidays, one strategy for reducing risk for those most vulnerable for bad outcomes should they become infected, is for everyone, including those at lower risk, to get the fall COVID bivalent booster and the flu vaccine soon. This is because those at lower risk, including children, can easily transmit both flu and COVID to those more vulnerable.”

Today, Public Health reported 6 additional deaths and 1,682 new positive cases. Of the 6 new deaths reported today, two people were between the ages of 50-64, two people were between the ages of 65-79, and two people were aged 80 years or older.  Of the six newly reported deaths, five had underlying health conditions. To date, the total number of deaths in L.A. County is 33,603.

Public Health has reported a total of 3,456,407 positive cases of COVID-19 across all areas of L.A. County. Today’s positivity rate is 4.3%.

There are 496 people with COVID-19 currently hospitalized. Testing results are available for more than 12,565,058 individuals, with 24% of people testing positive.

A wide range of data and dashboards on COVID-19 from the Los Angeles County Department of Public Health are available on the Public Health website at http://www.publichealth.lacounty.gov including:

Always check with trusted sources for the latest accurate information about novel coronavirus:

For more information:

Total Cases

Laboratory Confirmed Cases


— Los Angeles County (excl. LB and Pas)


— Long Beach


— Pasadena




— Los Angeles County (excl. LB and Pas)


— Long Beach


— Pasadena


Age Group (Los Angeles County Cases Only-excl LB and Pas)

– 0 to 4


– 5 to 11


– 12 to 17


– 18 to 29


– 30 to 49


– 50 to 64


– 65 to 79


–  over 80


–  Under Investigation


Gender (Los Angeles County Cases Only-excl LB and Pas)

–  Female


–  Male


–  Other


–  Under Investigation


Race/Ethnicity (Los Angeles County Cases Only-excl LB and Pas)

–  American Indian/Alaska Native


–  Asian


–  Black


–  Hispanic/Latino


–  Native Hawaiian/Pacific Islander


–  White


–  Other


–  Under Investigation


Hospitalization (Los Angeles County Cases Only-excl LB and Pas)

–  Hospitalized (Ever)


Deaths Race/Ethnicity (Los Angeles County Cases Only-excl LB and Pas)

–  American Indian/Alaska Native


–  Asian


–  Black


–  Hispanic/Latino


–  Native Hawaiian/Pacific Islander


–  White


–  Other


–  Under Investigation