Influenza surveillance

Oregon Influenza Season of 2000-2001

1) Epidemic Surveillance

Oregon State Public Health Laboratory

There were 77 cultures of epidemic catarrh that were found positive for influenza viruses among 335 such specimens tested at the OSPHL to "Rule out flu" for a recovery rate of 23%. Of these isolates, 30 (39%) were type A and 47 (61%) were type B viruses.

The first case was identified in an adult resident of Lane County from whom a specimen was obtained on 11/14/2000 and reported as positive for type B influenza virus by OSPHL during week 7 of the influenza 2000-2001 epidemiological year (October-September). Compared with the 10 previous seasons back to 1990-1991, week 7 ranks as number 6 and establishes the median for these 11 years (mean: 7.6; range: 2-14).

The duration of viral transmission extended over a sum of 16 weeks and ranked* as number 5 when compared as above with previous seasons (mean: 17.2; range: 11-26).

The total number of specimens ranked as a tie for first place as there were 335 specimens examined by OSPHL during the 1994-1995 season (mean: 538; range: 335-860). The fourth week of 2001 ranked as the peak week for receipt of specimens to "Rule out flu" with a total of 33.

The overall influenza virus recovery rate of 23% placed the season in a tie for 9th place with only the season of 1991-1992 ranking higher at 32% (mean: 16%; range: 4-32%). In comparison with 10 other previous seasons with cocirculating type A and B strains, 2000-2001 ranked as number 3 considering the total number of viral isolates (mean: 104; range: 12-187).

In summary, the season began and peaked a month earlier than historical norms and except for the above average virus recovery rate of 23%, it ranked at average to below average in all other respects.

Portland Area Healthcare Facilities

Providence Portland Medical Center Infectious Disease Laboratory staff, Kaiser Permanente Regional Laboratory staff together with the Nurse Epidemiologist of Kaiser Sunnyside Medical Center and Clinical Epidemiologists of Legacy Health System voluntarily submitted influenza case reports for both culture-confirmed as well as suspected influenza cases for the second consecutive season. Reports were received for 56 culture-confirmed cases and 23 suspected cases, including many with positive test results for viral antigen. The respective totals for 1999-2000 were 46 and 36.

Summary of Combined Reports

The reports from metro area healthcare facilities demonstrated once again their contributions to the more complete assessment of influenza morbidity in Oregon, especially among children under 5 years of age and older children aged 50 or more. Considering the two seasons, 43% of reports of patients with positive viral cultures from healthcare facilities originated among these two groups as opposed to 18% for reports from OSPHL. The total of 133 positive cultures from all sources represents a 75% increase over the total of 76 identified the previous season.

2. Vaccine Formulation for 2001-2002

The trivalent vaccine formulation for use in the United States during the 2001-2002 influenza season will consist of an A/Moscow/10/99 (H3N2)-like virus, an A/New Caledonia/20/99 (H1N1)-like virus and a B/Sichuan/379/99-like virus.

This formulation differs from that of the vaccine employed during the 2000-2001 season in light of the change in the B component. A/Panama/2007/99 is an A/Moscow/10/99 (H3N2)-like virus and will be employed for vaccine production. The type B component of vaccines will be represented by one or more of the following antigenically equivalent viruses selected because of growth properties: B/Johannesburg/5/99, B/Victoria/504/2000 or B/Guangdong/120/2000.

3. Interepidemic Surveillance

While this season has concluded, lab and epidemiological services are always available for unseasonal cases or clusters of influenza-like illness. Don't hesitate to call 503-731-4024.

* Rankings given in ascending order rather than descending.

06/25/2001

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