Detection and control of influenza outbreaks in well-vaccinated nursing home populations.

BACKGROUND: Influenza outbreaks continue to occur in nursing homes despite high vaccination coverage among residents. Recommendations for outbreak control in institutions such as nursing homes advises use of antiviral drugs to reduce influenza transmission. METHODS: Influenza surveillance was performed among elderly residents of nursing homes in Michigan during 2 influenza seasons. The antiviral drug oseltamivir was used for outbreak control at the discretion of nursing home staff once influenza transmission was confirmed by virus isolation or rapid antigen detection. RESULTS: During 2000-2001, influenza was not confirmed in any of the 28 participating homes, despite transmission of types A (H1N1) and B in the community. During 2001-2002, influenza type A (H3N2) transmission was confirmed in 8 (26%) of 31 participating homes; influenza vaccine coverage among residents was 57%- 98% in outbreak-associated homes. Oseltamivir was used in all homes with influenza transmission; outbreak control varied according to the rapidity of outbreak recognition and the extent of antiviral use. Reported adverse events were primarily gastrointestinal reactions and rashes. Analysis of the usefulness of rapid antigen detection tests for outbreak recognition indicated a sensitivity of only 77% (specificity, 92%). CONCLUSIONS: Oseltamivir was reasonably well tolerated, and its use, along with continued promotion of vaccination coverage among nursing home residents and staff, should be a valuable addition to institutional outbreak-control strategies.

Skin reactions in patients with influenza treated with oseltamivir: a retrospective cohort study.

Oseltamivir phosphate is an FDA-approved treatment for influenza that has been available for prescription use in the USA since 1999. The present report describes findings from a post-marketing safety study of skin reactions associated with oseltamivir use. All patients in the claims-derived Ingenix Research Database with a physician diagnosis of influenza and/or a dispensing of oseltamivir between 1 December 1999 and 31 March 2002 were identified. Cohort eligibility criteria included minimum baseline enrolment duration of 3 months, age of at least 1 year and no influenza vaccination on the date of influenza diagnosis or oseltamivir dispensing. Patients were classified into two primary cohorts, influenza diagnosis and oseltamivir dispensing on the same day, and influenza diagnosis but no oseltamivir at any time, and a cohort included for secondary analyses comprising patients who received an oseltamivir dispensing without an influenza diagnosis on the same day. Outcomes included general skin reactions and several specific skin reactions. Events occurring during the 30 days following the date of influenza diagnosis or oseltamivir dispensing were examined using Cox proportional hazards models. Model covariates included age, use of another influenza drug, month and year of index date, and use of antitussives. Adjusted rate ratios for the general class of skin reactions among the primary cohort of oseltamivir users versus non-users were 1.05 (95% CI: 0.88-1.24) for incident cases and 0.98 (95% CI: 0.77-1.24) among patients with a history of a skin reaction. Similar results were seen for the other skin reaction categories, and secondary analyses investigating the oseltamivir users without influenza revealed no elevation in risk. It is concluded that oseltamivir use does not appear to be associated with an increased risk of skin reactions.

Influenza infections after hematopoietic stem cell transplantation: risk factors, mortality, and the effect of antiviral therapy.

BACKGROUND: Community-acquired respiratory viruses, such as influenza virus, are thought to be major causes of morbidity and mortality in patients who had undergone hematopoietic stem cell transplantation (HSCT). Risk factors for acquisition, progression to pneumonia, and the effect of antiviral therapy are unknown. METHODS: We reviewed records from patients with documented influenza over 12 consecutive respiratory-virus infection seasons at a single transplantation center. RESULTS: From 1 September 1989 through 31 March 2002, influenza virus was isolated from 62 of 4797 persons undergoing HSCT (1.3%); 44 patients had upper respiratory tract infections (URIs) alone, and 18 developed pneumonia. Among patients with influenza virus infection, pneumonia developed more commonly among those infected earlier after transplantation (median, 36 vs. 61 days, P=.04) and those with concurrent lymphopenia. Of the 51 cases that were initially diagnosed as URIs, 17 were treated with antivirals, and 34 were not treated. Six untreated patients (18%) developed pneumonia, whereas 1 (13%) of 8 patients treated with rimantadine and 0 of 9 treated with oseltamivir developed pneumonia. The duration of influenza virus shedding was longer in patients treated with steroid doses of >1 mg/kg than among those treated with doses of <1 mg/kg (mean, 15 vs. 9 days); there was a trend towards decreased shedding with oseltamivir therapy (but not rimantadine therapy) after controlling for steroid use (P<.08). The 30-day mortality rate was highest among patients who had progression to pneumonia (5 [28%] of 18 patients); pulmonary copathogens (such as Aspergillus fumigatus) were commonly isolated. CONCLUSIONS: Influenza virus infection is an important cause of mortality early after HSCT. Our nonrandomized data suggest that early antiviral therapy with neuraminidase inhibitors may prevent progression to pneumonia and decrease viral shedding, which may prevent both influenza-related death in index patients and nosocomial transmission to others.

Use of oseltamivir during influenza outbreaks in Ontario nursing homes, 1999-2000.

OBJECTIVES: To describe the experience of Ontario long-term care facilities that used oseltamivir during influenza outbreaks in 1999/2000. DESIGN: Case series. SETTING: Ten Ontario long-term care facilities for older people and their residents. PARTICIPANTS: Older residents of long-term care facilities. INTERVENTION: Oseltamivir for treatment or prophylaxis during 11 influenza outbreaks in 1999/2000. MEASUREMENTS: Control of outbreaks; pneumonia, hospitalization, and death complicating acute influenza. RESULTS: All outbreaks were due to influenza A//H3N2/Sydney/05/97. One facility elected to use oseltamivir for treatment and amantadine for prophylaxis. The remaining nine facilities (10 outbreaks) recommended oseltamivir for treatment and prophylaxis (after amantadine failure in five and as primary prophylaxis in five). Use of oseltamivir was associated with termination of the outbreak in all eight evaluable outbreaks. Overall, 178/185 (96%) case-residents met the case definition of influenza and had complete data for evaluation. Of these, 63 (35%) were treated with antibiotics, 37 (21%) were diagnosed with pneumonia, 19 (11%) were hospitalized, and 16 (9%) died. Compared with residents receiving no therapy or who became ill while taking amantadine, residents who received oseltamivir within 48 hours of the onset of symptoms were less likely to be prescribed antibiotics, to be hospitalized, or to die (P <.05 for each outcome). These differences persisted and remained statistically significant when corrected for influenza immunization status. A total of 730 residents received oseltamivir prophylaxis for a median of 9 days (range 5-12). Of these, side effects were identified in 30 (4.1%), the most common being diarrhea (12 residents, 1.6%), cough (5, 0.7%), confusion (4, 0.5%) and nausea (4, 0.5%). CONCLUSIONS: Oseltamivir is safe and appears to be effective when used as treatment or prophylaxis to control outbreaks of influenza in older nursing home residents.