CDPH Influenza Surveillance Program

The California Department of Public Health (CDPH) Influenza Surveillance Program is a collaborative effort between CDPH, the Centers for Disease Control and Prevention (CDC), Kaiser Permanente, California local health jurisdictions and the participating California sentinel providers and sentinel laboratories. Influenza surveillance in California is particularly important due to its coastal location with several ports of entry for flights and shipping from Asia. Annual influenza epidemics follow a winter seasonal pattern in the United States with typical activity peaking during late December to early February. CDPH obtains and analyzes clinical, pharmacy and laboratory data year-round in an effort to determine the timing and impact of influenza activity and to determine how well circulating strains of the virus match those used in the current influenza vaccines. Each surveillance method is described more fully below.

CDC Influenza Sentinel Providers

Sentinel providers (physicians, nurse practitioners, and physician assistants) situated throughout California report the number of outpatient visits for influenza-like illness (ILI) and the total number of visits per week. ILI is defined as any illness with fever (>100F or 37.8C). AND cough and/or soure throat (in the absence of a known cause).This data is reported weekly as a percentage of total visits. At present, over 150 Sentinel Providers report ILI data and submit specimens to CDPH for further testing, allowing CDPH to attain the CDC goal of 1 sentinel provider per 250,000 population. Further information about enrolling in the Sentinel Provider program can be found at: http://www.cdph.ca.gov/programs/dcdc/Pages/CaliforniaSentinelProviderProgram.aspx

Kaiser Inpatient Data

The Kaiser Permanente healthcare system provides medical care throughout the state to over one sixth of California residents. Thus, it is reasonable to assume that influenza activity among Kaiser patients reflects the influenza activity for the entire state. Inpatient discharge diagnoses of "pneumonia" and "influenza" (ICD-9 480-487) have been used to examine influenza trends in California; however, these data cannot be obtained in real time. In contrast, inpatient admission diagnoses are entered daily by text string and can be accessed the following day. Admission diagnoses of flu, pneumonia, and influenza ("flu admits") serve as surrogate markers for the more accurate discharge diagnoses. Influenza activity is tracked by dividing the number of flu admits by the total number of hospital admissions for the same day, thereby obtaining a percentage of influenza admissions. Admissions for pregnancy, labor and delivery, birth, and outpatient procedures are excluded from the denominator. Influenza admissions that have subsequent laboratory confirmation for influenza are also tracked; however there is a delay in reporting of approximately 1-2 weeks due to time required for testing.

Kaiser Permanente Pharmacy Data

The number of prescriptions for drugs active against influenza, such as amantadine, rimantadine, zanamivir and oseltamivir, are used to serve as indicators of influenza activity. This component of the project assesses the number of influenza antiviral prescriptions filled weekly by all Kaiser outpatient pharmacies in California.

Severe and Fatal Influenza Case-Based Surveillance

Public health monitoring of severely ill cases of all types and subtypes of influenza is important for monitoring for the circulation of novel influenza viruses that may cause future pandemics and to characterize populations at risk for complications. Information gathered from surveillance can lead to new prevention measures, education campaigns, and strategies for vaccine and antiviral use that will help protect the public. CDPH is working with the local health jurisdictions to enhance surveillance and to amend current reporting regulations for influenza according to the California reportable disease list for medical providers (Section 2500)

Currently, the following cases are reportable:

• Influenza deaths in laboratory-confirmed cases for ages 0- 64 years

In addition, CDPH requests that the following cases are reported on a voluntary basis:

• Laboratory-confirmed influenza cases ages 0-64 years requiring intensive care

Laboratory confirmation can include any positive test performed by any clinical, commercial or local public health laboratory (LPHL), including by positive rapid antigen test (as rapid antigen tests may yield a relatively high proportion of false positive results when influenza prevalence is low, it is recommended that a positive rapid antigen test result be followed up with confirmatory testing using one of the other indicated methods), direct fluorescence assay, culture or polymerase chain reaction (PCR).

Laboratory Surveillance

The laboratory component of the project involves use of data from hospital, academic, private and public health laboratories located throughout California. These laboratories report the number of laboratory-confirmed influenza and other respiratory virus detections and isolations on a weekly basis. Reporting laboratories are divided into the following networks:

The Respiratory Laboratory Network (RLN) is composed of 24 local public health laboratories that offer PCR testing for influenza A and B and testing using the R-mix shell vial culture system to identify five other common respiratory viruses (RSV, adenovirus, parainfluenza virus type 1-3). Participating laboratories in the 2010-11 season include: Contra Costa, El Dorado, Fresno, Long Beach, Los Angeles, Marin, Monterey, Orange, Placer, Riverside, Sacramento, San Bernardino, San Diego, San Francisco, San Joaquin, San Luis Obispo, San Mateo, Santa Barbara, Santa Clara, Shasta, Solano, Sonoma, Tulare, Ventura

California Sentinel Laboratories are a network of clinical, commercial, academic and hospital laboratories located throughout California that provide weekly data on the number of laboratory-confirmed influenza and other respiratory virus detections and isolations. These labs use various testing methods, including rapid test, direct fluorescent assay, viral culture and polymerase chain reaction (PCR). Participating laboratories in the 2010-11 season include: North Kaiser Regional Laboratory, Stanford Medical Center, Mt. Zion/UCSF, San Francisco General Hospital, Children’s Hospital Oakland, UCLA Medical Center, Long Beach Memorial Hospital, San Diego Children’s Hospital, Clinicas de Salud del Pueblo – Brawley, Clinicas de Salud del Pueblo - Calexico, San Ysidro Health Center and Valley Children’s Hospital (central CA)

The CDPH Viral and Rickettsial Laboratory (VRDL) serves as a reference laboratory for the State of California. A fraction of the influenza viruses isolated at participating laboratories are forwarded to VRDL for further antigenic and genetic characterization. Complete antigenic characterization enables detection of new strain variants and provides a method for monitoring how well circulating influenza strains match those used in the current influenza vaccines. In addition, sentinel physicians located throughout California submit specimens from patients with influenza-like illnesses for respiratory virus PCR and straintyping at VRDL. The VRDL performs surveillance for antiviral resistance on a limited basis and can also test individual cases on special request. The VRDL works closely with the RLN and the CDC to develop and adapt new assays for novel influenza viruses and other emerging pathogens.