Viral Respiratory Surveillance for LA County


Los Angeles (LA) County Department of Public Health (DPH) collects information on indicators of COVID-19, influenza, and Respiratory Syncytial Virus activity year-round. These indicators track the intensity, spread, and temporal trends of viral respiratory illness in LA County.

The weekly surveillance data presented here are preliminary and subject to change.

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Respiratory Surveillance At-a-Glance

LAC DPH prepares this report to summarize current respiratory illness surveillance data in LAC*. Weekly surveillance data are preliminary and subject to change. More information regarding methods can be found on the surveillance system specific pages of this report.

Daily counts of COVID-19 cases and deaths can be found on the COVID-19 Surveillance Dashboard.

*LAC DPH surveillance data excludes the cities of Long Beach and Pasadena.

*For information on trend indicator arrows, see Technical Notes.


Viral surveillance data is provided by clinical laboratories serving hospitals and healthcare networks across Los Angeles County. Participating laboratories provide the number of positive tests and total number of specimens tested for SARS-Cov-2, influenza and respiratory syncytial virus. Data reported from viral surveillance laboratories will differ from the overall county testing data because of differences in the population tested, types of tests used, and changes in the number of laboratories conducting testing over time.

*LAC DPH surveillance data excludes the cities of Long Beach and Pasadena.

*The respiratory virus surveillance period starts with MMWR week 40 and runs through week 39 of the following year. The 2023-24 season started on Oct 1, 2023.

**Baseline is defined as mean percentage of specimens testing positive during non-influenza weeks for the previous three seasons plus two standard deviations. Non-epidemic weeks are periods of ≥2 consecutive weeks during which each week accounted for <2% of the season’s total number of specimens that tested positive. The COVID-19 pandemic affected the circulation of other respiratory viruses. Pandemic weeks are excluded from the baseline calculation.

Wastewater Surveillance

Wastewater data includes data from the joint Water Pollution Control Plant, Hyperion, and Lancaster sewersheds. Data comes from the WastewaterSCAN collaborative. Data are normalized average wastewater SARS-CoV-2 concentrations. A weighted average is calculated by using the SARS-CoV-2 viral concentrations across 3 sewer systems that track the virus in LA County (Hyperior Water Reclamation Plant, Joint Water Pollution Control Plant, Lancaster Water Reclamation Plant), with the weights representing the population size served by each sewer system.

For more information on wastewater surveillance of Influenza A, see CDPH's Frequently Asked Questions about Wastewater Surveillance for Influenza A Viruses.

*A technical issue with influenza A assay data for the 2023-2024 season has been identified, which has impacted the results for influenza A concentrations in wastewater. The influenza A data for the 2023-2024 season will be updated as the data becomes available.

Emergency Department

Public Health's Syndromic Surveillance Project monitors initial self-reported symptoms as well as diagnosis codes from patients presenting to participating emergency departments throughout LAC. These symptoms are categorized into different clinical syndromes according to specific search terms. Visits are included in the coronavirus category if the chief complaint or diagnosis terms include any mention of "COVID," "Coronavirus" or similar key words. The syndrome of ILI is defined as mention of influenza; or fever (subjective or measured greater than 100° F) plus cough or sore throat. The ILI and coronavirus classified ED visits for all ages and by age group are analyzed weekly and year-round. The coronavirus and ILI categories are not mutually exclusive.

Emergency Department Visits for COVID-19 by Age Category
Emergency Department Visits for COVID-19, 2020-2024 Flu Seasons
Emergency Department Visits for Influenza-Like Illness by Age Category
Emergency Department Visits for Influenza-Like Illness, 2020-2024 Flu Seasons

*The grey bar represents a two week period when syndrome classifications (e.g. for COVID, ILI, etc.) are in flux due to delayed diagnosis information -- these percentages are preliminary and subject to increase.

Influenza Hospitalizations

Influenza hospitalizations are reported weekly by hospitals through the CDC’s National Healthcare Safety Network (NHSN). The data shows the number of total influenza hospitalizations in Los Angeles County by ICU admission status, and the 7-day average of new patient hospitalizations. The 7 day average for new patients hospitalized is calculated by taking the average of the number of new influenza positive patients that were hospitalized over a 1-week period.

Angelenos in Action

Angelenos in Action is a voluntary text-based public health survey that collects information to monitor COVID-19 symptoms across LA County in real time. Volunteers across LA County provide information on their health as part of a weekly SMS survey. Respondents are assigned to a random day, and then texted once per week about their symptoms. Rates are then calculated weekly.


Each week, LAC DPH reports the total number of death certificates received and the number of those for which pneumonia, influenza, or COVID-19 (PIC) was listed as the underlying or contributing cause of death by age group. Technical note: the number of deaths reported in recent weeks does not represent all deaths that occurred in the reporting period. Data may be incomplete due to a lag between when the death occurred and when the death was registered. Previous weeks counts or percentages may change as vital records are updated with lagged death certificates. This analysis includes all certificates of death (excluding fetal deaths) occurring in the County of Los Angeles (excluding Long Beach and Pasadena) regardless of the residence of the deceased.

* Table includes deaths in which influenza was listed as a primary or contributing cause of death. Providers are mandated to report Influenza-associated deaths in persons aged <18 years. Public Health reviews all provider reported and death certificate identified deaths in persons aged <18 years to confirm that the cause of death was compatible with influenza.

**The seasonal baseline of pneumonia, influenza, and COVID-19 (PIC) deaths is calculated using a periodic regression model that incorporates a robust regression procedure applied to data from the previous 5 years. An increase of 1.645 standard deviations above the seasonal baseline of PIC deaths is considered the “epidemic threshold,” i.e., the point at which the observed proportion of deaths attributed to pneumonia, influenza or COVID-19 was significantly higher than would be expected at that time of the year in the absence of substantial virus-related mortality.

SARS-CoV-2 Variants of Concern

To track the circulation of SARS-CoV-2 variants in Los Angeles County, DPH receives whole genome sequencing results for specimens collected from Los Angeles County residents. Data presented here come from the LAC DPH Public Health Laboratory, clinical, commercial, and academic laboratory partners. The proportion of cases sequenced varies over time; generally sequencing results are available for 12-16% of reported cases. Whole genome sequencing data has a reporting lag time of 2-3 weeks.

*Includes descendant lineages except where otherwise specified.

Technical Notes

Trend Indicators:
Clinical Labs: The up and down arrows indicate a change of at least 0.5 percentage points in the percentage of specimens positive for influenza, COVID-19, or RSV compared to the previous week reported by LAC sentinel surveillance laboratories.
Emergency Department: The up and down arrows indicate a change of at least 0.1 percentage points in the percentage of COVID-19 and ILI classified emergency department visits in LAC compared to the previous week.

Note about weeks: We present Morbidity and Mortality Weekly Report (MMWR) weeks. The MMWR week corresponds with the week of the epidemiologic year for which the National Notifiable Diseases Surveillance System (NNDSS) disease report is assigned. The MMWR week is used by local or state health departments for the purposes of MMWR disease incidence reporting and publishing. Each MMWR week begins Sunday and ends the following Saturday.

The respiratory virus surveillance period starts with MMWR week 40 and runs through week 39 of the following year. The 2023-24 season started on Oct 1, 2023.

For more detailed data on COVID-19 in LA County, please visit the COVID-19 Data Page.

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