Influenza surveillance

Oregon Influenza Season of 2002-2003

1) Epidemic Surveillance

Oregon State Public Health Laboratory

There were 31 cultures of epidemic catarrh found positive for influenza viruses among 224 such specimens tested at the OSPHL to "Rule out flu" for a recovery rate of 14%. Of these isolates, 7 (23%) were type B and the rest were type A viruses.

The earliest case by virtue of the date of effluvia collection on 11/16/02 was identified as type A influenza in a 15-year-old resident of Yamhill County, a patient of Willamette Valley Medical Center. The positive culture was reported by OSPHL on 11/29/02. No other cases were reported until sustained community transmission commenced during fluweek #13 of the influenza 2002-2003 epidemiological year (October-September). Compared with weekly reports for the 11 previous seasons back to 1991-1992, fluweek #13 ranks as a tie with the season of 1997-1998 for the latest seasonal start (mean: 7.6; range: 2-13). The last confirmed case was reported on 04/14/03 during fluweek #29 and the specimen was harvested on 03/31/03.

The duration of viral transmission extended over a sum of 16 weeks and ranked as a tie for number 4 when compared as above with previous seasons (mean: 17.3; range: 11-26). The other season of 16 weeks duration occurred in 2000-2001.

The total number of specimens ranked as number 1* in fewest specimens processed since the season of 1991-1992 (mean: 495; range: 224-860). Last season ranked as number 3 with 388. The eighth week of 2003 (third week in February) ranked as the peak week for receipt of specimens to "Rule out flu" with a total of 23. The peak week last season occurred one week earlier with receipt of 40 specimens.

The overall influenza virus recovery rate of 14% placed the season in 4th* place (mean: 17%; range: 4-32%) with only the seasons of 1994-95, 1999-00 and 2001-2002 ranking lower at 4%, 6% and 11%, respectively. In comparison with seasons back to 1987-1988, this season's 31 influenza viral isolates ranked in a tie with 1980-1981 for the fewest at #4 (mean: 85; range: 9-187).

In summary, the 2002-2003 season was exceptionally mild with respect to epidemiologic comparisons with earlier epidemics as far back as 1987-1988.

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 fourth consecutive season. PPMCIDL staff also voluntarily reported the results of all tests for respiratory viruses from November through April. These data were posted on the Oregon Health Services influenza website along with the OSPHL data on a weekly basis.

The first report of a culture-confirmed case of influenza was received from PPMCIDL on 01/02/03. The 63-year-old patient with type A influenza was a resident of Curry County. LHS followed with the first report of type B influenza on 01/07/03. The last culture-confirmed case was reported on 04/16/03 by PPMCIDL. The 28-year-old patient, a resident of Washington County, was examined on 04/10/03 and found to have type B influenza.

In all, 40 reports of positive cultures were received, 34 type A and 6 type B compared with 67 type A and 3 type B last season. Twenty-two reports were received from LHS and 18 from PPMCIDL. In the three previous seasons, the totals were 70 in 2001-02 (LHS 12, PPMCIDL 58), 56 in 2001-01 (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 three 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 four seasons, 47% (101/213) of reports of patients with positive viral cultures from healthcare facilities originated among these two groups as opposed to 20% (36/176) for reports from OSPHL. 

The total of 71 positive cultures from all sources represents a 34% decrease from the average of 108 for the previous three seasons.

2) Vaccine Formulation for 2003-2004

The trivalent vaccine formulation for use in the United States during the 2003-2004 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 does not differ from that of the vaccine employed during the 2002-2003 season. No vaccine obtained for use in 2002-2003 should be used past its expiration date.

3. Interepidemic Surveillance

Due to the threat of recent epizootics caused by avian influenza viruses in Asia and Europe and the occurrence of human infections, laboratory surveillance at the Oregon State Public Health Laboratory will continue through the summer and into the 2003-2004 season. Specimens to "Rule out flu" will continue to be accepted and cultured for influenza virus free of charge. Virus transport kits may be acquired by calling 503-229-5882. In addition, 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 05/30/03

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