Welcome to the State of California 
H1N1 Data Banner

This Web page is no longer being maintained or updated; it is provided for historical purposes only. For current information on seasonal influenza (flu), see the California Department of Public Health Influenza Web page.

 Related H1N1 Data

 H1N1 Flu Information

H1N1 Flu Data and Statistics

Weekly California H1N1 Flu Summary Data

Reported ICU and Fatal Cases of 2009 H1N1 Influenza Infections in California (as of August 28, 2010)

ICU cases
and Deaths




Weekly Number of Fatal 2009 H1N1 Influenza Cases in California by Week of Death, Week Ending April 28, 2009 - August 28, 2010

H1N1 Graphs

 H1N1 Flu Graphs

For more information, see:
CDPH Enhanced Surveillance for 2009 H1N1 Influenza Virus (PDF) Opens new browser - Week ending April 3, 2010

Monthly Provisional H1N1 Flu Data Tables by Local Health Jurisdiction

Provisional Data Tables - Reported hospitalizations, ICU cases, and deaths by local health jurisdiction, plus historical data tables (updated August 28, 2010)

Provisional Maps - Historical maps of reported cases by local health jurisdiction (maps discontinued as of July 16, 2009)

Information About Data Posting on This Website

Starting September 27, H1N1 Flu Provisional Data Tables will be posted to this website on a monthly basis (for example, data for November will be posted during the first week of December). The summary statewide H1N1 Flu data (table on this page) will continue to be udpated weekly on Thursdays.

All data is considered provisional and is subject to change.  Local Health Jurisdictions include the 58 California county health departments and 3 city health departments (Berkeley, Long Beach, and Pasadena). The city health department jurisdiction data are not included in the county jurisdiction totals.

Surveillance System

Changes in H1N1 Flu Data Reporting

CDPH continues to perform surveillance and provide PCR testing for influenza, confirmatory testing for H1N1 flu 2009, and guidance and assistance to our local public health partners. Effective July 15, 2009, local health departments were no longer asked to report outpatient cases. Effective August 12, 2009, local health departments were asked to report hospitalized cases of H1N1 flu as weekly aggregate numbers. Intensive care unit cases and fatal cases will continue to be reported with individual case report forms. Effective September 8, 2009, CDPH changed the timeframe for reporting H1N1 flu cases. In response to requests from local health jurisdictions (LHJs), CDPH now uses a reporting week consistent with the MMWR week, namely Sunday through Saturday, rather than the Tuesday to Tuesday reporting week previously in place. Effective March 6, 2010, CDPH reported H1N1 flu data on a monthly basis. LHJs will continue to report their weekly data to CDPH every Tuesday by 12:00 pm. Effective May 1, 2010, reporting of aggregate data on hospitalized cases of 2009 H1N1 flu is no longer required.

CDPH case report forms should continue to be submitted for indifiduals with probable or confirmed 2009 H1N1 flu who require hospitalization in an intensive care unit (ICU cases) or who die (fatal cases). Individuals who are positive for influenza A by PCR and negative for seasonal human subtypes H1 and H3 (i.e., unsubtypeable) are considered probably 2009 H1N1 flu cases. Individuals who test positive by a 2009 H1N1 influenza-specific PCR are considered confirmed 2009 H1N1 flu cases.

The reported number of cases of H1N1 flu in California do not reflect how many actual cases there may be in the state because individuals in outpatient settings are no longer being tested for the presence of the virus and many cases go undetected due to the mild nature of disease among most people. Laboratory testing is limited to individuals with serious H1N1 flu illness, including hospitalized patients, and those at high risk for complications.

Additional Information About H1N1 Flu Surveillance and Reporting 
  • Interim Guidance for State and Local Health Departments for Reporting Influenza-Associated Hospitalizations and Deaths for the 2009-2010 Season - CDC, September 8, 2009
    Last modified on: 8/25/2011 12:54 PM