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Oregon Influenza Season of 2001-2002
1. Epidemic Surveillance
Oregon State Public Health Laboratory
There were 44 cultures of epidemic catarrh found positive for influenza viruses among 377 such specimens tested at the OSPHL to "Rule out flu" for a recovery rate of 11%. Of these isolates, one was a type B virus and the rest were type A viruses.
The earliest case by virtue of onset on 11/25/01 was identified by culture of effluvia taken from a 44 year old on 11/26/01 and submitted by St. Charles Medical Center. The culture was reported positive for type A(H3N2) virus by OSPHL on 12/07/01 during week 10 of the influenza 2001-2002 epidemiological year (October-September). Compared with weekly reports for the 10 previous seasons back to 1991-1992, week 10 ranks as a tie for the 3rd latest seasonal start (mean: 6.9; range: 2-13). The last confirmed case was reported on 04/17/02 during week 29 and onset was given as 03/12/02.
The duration of viral transmission extended over a sum of 19 weeks and ranked as number 3 when compared as above with previous seasons (mean: 17.3; range: 11-26). The two longer seasons were 1994-95 at 20 weeks and 1992-93 at 26 weeks.
The total number of specimens ranked 3rd* in fewest specimens with only two other seasons having fewer specimens submitted, 1994-1995 with 335 and 2000-01 with 336 (mean: 530; range: 335-860). The fourth week of 2002 ranked as the peak week for receipt of specimens to ARule out flu@ with a total of 40, the same week as last season with a high of 33.
The overall influenza virus recovery rate of 11% placed the season in 3rd* place with only the seasons of 1994-95 and 1999-00 ranking lower at 4% and 6%, respectively (mean: 17%; range: 4-32%).
In summary, the season began later and lasted longer than the average for the last 10 seasons. In all other respects it fell below average and could only be characterized as a very mild season.
Portland Area Healthcare Facilities
Providence Portland Medical Center Infectious Disease Laboratory (PPMCIDL) staff, Kaiser Permanente Regional Laboratory (KPRL) staff together with the Nurse Epidemiologist of Kaiser Sunnyside Medical Center and Clinical Epidemiologists of Legacy Health System (LHS) voluntarily submitted influenza case reports for both culture-confirmed as well as suspected influenza cases for the third consecutive season.
The first report of a culture-confirmed case of influenza was received from PPMCID on 12/04/02. The 4-year-old patient was a resident of Washington County. The last culture-confirmed case was reported on 04/15/02 by LHS. The 2-year-old patient, a resident of Washington County, was admitted on 04/07/02.
In all, 71 reports of positive cultures were received, 67 type A and 4 type B. Twelve reports were received from LHS and 58 from PPMCIDL. In the two previous seasons, the totals were 56 in 2000-01 (KPRL 2, LHS 13, PPMCIDL 41) and 46 in 1999-00 (LHS 28, PPMCIDL 18). Additional reports were submitted for symptomatic patients admitted with flulike illness and/or testing positive for influenza antigens. These reports also fell well below numbers for the two previous seasons.
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 three seasons, 49% (84/170) of reports of patients with positive viral cultures from healthcare facilities originated among these two groups as opposed to 19% (27/142) for reports from OSPHL.
The total of 115 positive cultures from all sources represents an 14% decrease from the total of 133 identified the previous season.
2. Vaccine Formulation for 2002-2003
The trivalent vaccine formulation for use in the United States during the 2002-2003 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/Hong Kong/330/2001-like virus.
This formulation differs from that of the vaccine employed during the 2001-2002 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 as last year. The type B component of vaccines will be a B/Hong Kong/330/2001-like virus as opposed to the B component of last year=s vaccine, a B/Sichuan/379/99-like virus.
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.
ODHS/HS/ODPE/ACDP 06/04/02 Oregon State Public Health Laboratory |
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