The summary countywide data will continue to be updated. All data are considered provisional and are subject to change.

Highlights for Week 46 (November 18, 2009)

• In the past seven weeks, all specimens tested for influenza at the Santa Clara County Public Health Lab were influenza A, unsubtypable (probable H1N1).
• The outpatient clinics reporting to through the California Sentinel Provider Program indicates that 6% of their patients are presenting with influenza-like illness (ILI). This is comparable to the national data is 6.7%, which is above the national baseline average of 2.3% reported in previous years.
• School surveillance is showing a decrease in the percent of students absent due to illnesses.

INFLUENZA CASE REPORTING

Novel H1N1 influenza A, now known as 2009 Pandemic H1N1 influenza, was initially made reportable in April 2009. From April to July 2009, all H1N1 confirmed and probable cases – both outpatient and hospitalized – were reported to the local health department. Beginning in July, only hospitalized cases were reportable and counted, and effective mid-August, the California Department of Public Health (CDPH) initiated weekly aggregate reporting for all hospitalized cases of influenza. Since aggregate reporting began, the date of symptom onset is not collected on hospitalized cases. Now, only ICU and fatal cases are reported individually. Both aggregate weekly hospital reports and individual case reports are submitted to the California Department of Public Health (CDPH).

The number of influenza cases reported below captures severe cases that have resulted in hospitalization and reflects only a portion of the actual number of influenza cases in Santa Clara County. Laboratory testing is limited to individuals with serious H1N1 illness, including hospitalized patients, and those at high risk for complications.

Table 1: Cumulative number of influenza (H1N1 and other influenza) cases by hospitalization, ICU and deaths, reported in Santa Clara County and California. Reporting period: April 2009 to Week 46 (November 18, 2009).

Table 2: Cumulative number of hospitalized influenza (H1N1 and other influenza) cases reported in Santa Clara County, by age group. Reporting period: April 2009 to Week 46 (November 18, 2009).

Figure 1: Hospitalized and ICU influenza (H1N1 and other influenza) cases reported to Santa Clara County Public Health Department by week of report. Reporting period: April 2009 - Week 46 (November 18, 2009).

Figure 2: Deaths associated with pandemic H1N1 influenza reported to Santa Clara County Public Health Department, by week of death. Reporting period: April 2009 - Week 46 (November 18, 2009).

SYNDROMIC SURVEILLANCE

ESSENCE (Electronic Surveillance System for the Early Notification of Community-Based Epidemics), is a real time, automated syndromic surveillance system that collects chief complaint data from Emergency Department visits at five Santa Clara County hospitals. The hospitals represented by this system include Columbia Good Samaritan, O’Connor Hospital, Regional Medical Center, St. Louise Regional Hospital, and Valley Medical Center.

Figure 3: Number of visits to Santa Clara County hospital emergency departments for a respiratory syndrome*, in patients age <18, by date of visit. Reporting period: past 90 days from Week 46 (November 18, 2009).

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Figure 4: Number of visits to Santa Clara County hospital emergency departments for a respiratory syndrome* in patients age >=18, by date of visit. Reporting period: past 90 days from Week 46 (November 18, 2009).

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* Respiratory syndrome includes: Acute Bronchitis, Lower Respiratory Infection Bronchitis, Otitis Media, Chest Congestion, Pneumonia, Nasal Congestion, Shortness Of Breath, Cough, SoreThroat, Difficulty Breathing, Upper Respiratory Infection, Hemoptysis, Wheezing, Laryngitis.

LABORATORY SURVEILLANCE

Table 4: Virologic Surveillance Data, Santa Clara County Public Health Laboratory. Reporting period: Week 17 (April 27, 2009) – Week 45 (November 9-13, 2009).

Figure 5: Influenza testing results, by subtype and week of specimen submission to the Santa Clara County Public Health Laboratory. Reporting period: April 2009-Week 45 (November 2-6, 2009).

SENTINEL PROVIDER INFLUENZA SURVEILLANCE

The California Sentinel Provider Influenza Surveillance Program is a partnership between clinicians, local health departments (LHDs), the California Department of Health Services (CDPH), and the federal Centers for Disease Control and Prevention (CDC) to conduct surveillance for influenza-like illness (ILI). Providers of any specialty in any type of practice are eligible to be sentinel providers. The information provided by the sentinel providers show the impact of influenza-like Illness in the outpatient population.

Figure 6: Number of patients seen by reporting Santa Clara County sentinel providers and the percentage of patients with Influenza-Like Illnesses (ILI). Reporting period: January 2009 to Week 45 (November 8-14, 2009).

Figure 7: Total Number of Patients Presenting with Influenza-Like Illnesses (ILI), by Age Group. Reporting period: January 2009 to Week 44 (November 1-7, 2009).

SCHOOL SURVEILLANCE

At the beginning of the school year, eighteen schools agreed to participate in school absentee surveillance. Currently, 21 schools participate. Schools report the number of students absent due to illness. This information is only a sample of schools in Santa Clara County and provides a limited picture of the illness trends in schools.

Figure 8. Percent of elementary school students absent due to illness. Reporting period August 19, 2009 to Week 45 (November 17, 2009).

Figure 9. Percent of high school students absent due to illness. Reporting period August 19, 2009 to Week 46 (November 17, 2009).