Surveillance Lessons from First-wave Pandemic (H1N1) 2009, Northern California, USA

EID Journal Home > Volume 16, Number 3–March 2010

Volume 16, Number 3–March 2010
Dispatch
Surveillance Lessons from First-wave Pandemic (H1N1) 2009, Northern California, USA
Roger Baxter
Author affiliation: Kaiser Permanente Vaccine Study Center, Oakland, California, USA

Suggested citation for this article

Abstract
After the appearance of pandemic (H1N1) 2009 in April 2009, influenza activity was monitored within the Kaiser Permanente Northern California division by using laboratory, pharmacy, telephone calls, and utilization (services patients received) data. A combination of testing and utilization data showed a pattern of disease activity, but this pattern may have been affected by public perception of the epidemic.

In April 2009, the novel swine-origin H1N1 influenza virus, now referred to as pandemic (H1N1) 2009 virus, was identified in the United States in California and in Mexico. During April, increasing numbers of cases were identified in Mexico, and sporadic cases were seen in the United States, mostly in returning travelers (1). Media coverage was high, and the public and medical communities were alert to the presence of the novel virus (2). Although the World Health Organization raised its influenza alert level to phase 6 (calling this a true pandemic) on June 11, by this time media attention in the United States had waned, and concern was for reemergence in the fall (3). However, virus activity did not diminish in northern California; rather, pandemic (H1N1) 2009 influenza remained active at high levels.

Kaiser Permanente (KP) is a medical care organization with 3.2 million members in its Northern California division (KPNC). Members receive essentially all medical care from KP providers and in KP facilities. An electronic medical record system records diagnoses from outpatient and emergency department visits and hospitalizations, as well as medications, immunizations, and ancillary services received by patients. A central laboratory in Berkeley performs all microbiologic and virologic testing. In addition, all telephone callers to the system are routed to central call centers, where information is gathered on whether the caller is asking influenza-related questions. This report details the recent experience of pandemic (H1N1) 2009 in KPNC and documents KP surveillance efforts.

The Study
Influenza testing was performed by using a real-time PCR for influenza A and B and respiratory syncytial virus on nasopharyngeal swabs. Similar methods have been shown to be superior to other tests and sensitive and specific for detecting pandemic (H1N1) 2009 influenza (4). A weekly report went to primary care providers, advising on current viral activity, and gave guidelines for testing and treating. All specimens positive for influenza A were transported to the California State Department of Public Health laboratory for H1N1 confirmation testing early in the pandemic, but testing was later restricted to specimens from hospitalized patients only. Results of testing were provided weekly with counts from the previous week, Sunday through Saturday. Hospitalization rates were counted weekly by using text strings from admission diagnoses for pneumonia or influenza. If KPNC members had questions regarding influenza, when they called for advice or appointments they were triaged to the "flu queue," where they could receive prerecorded messages or one-on-one advice with a nurse or physician. We plotted the percentage of all calls per week that were counted as influenza related. Weekly counts of medical office visits for influenza-like illness (ILI)—fever, influenza, or upper respiratory infection—were also plotted. The study was reviewed and approved by the Kaiser Permanente and our Institutional Review Boards.

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http://www.cdc.gov/eid/content/16/3/504.htm

Suggested Citation for this Article
Baxter R. Surveillance lessons from first-wave pandemic (H1N1) 2009, northern California, USA. Emerg Infect Dis [serial on the Internet]. 2010 Mar [date cited]. http://www.cdc.gov/EID/content/16/3/504.htm

DOI: 10.3201/eid1603.091285