Experience with a rapid diagnostic test for influenza

Influenza vaccination and antiviral therapy: is there a role for concurrent administration in the institutionalised elderly?

Influenza vaccination is estimated to be 50-68% efficacious in preventing pneumonia, hospitalisation or death in nursing home residents. Large culture-proven outbreaks may occur despite high resident vaccination rates. There is, therefore, a significant role for concurrent administration of influenza vaccination and antiviral therapy. The use of antiviral treatment and chemoprophylaxis requires community reporting of viral isolates, and contingency plans for rapid case identification and application of antiviral therapy. Clinicians must react quickly to control a highly infectious seasonal pathogen that may strike as an explosive outbreak. This situation is unique in geriatric practice. Current antiviral treatment should be administered within 48 hours of symptom onset, and is more efficacious if administered within 12 hours. In the case of an explosive institutional outbreak, a 1-day delay in prophylaxis may allow infection of many residents with a potentially fatal illness. Influenza must be differentiated from other respiratory viruses or syndromes. Grouped rapid diagnostic tests can aid laboratory confirmation. Antiviral agents include the M(2) inhibitors, amantadine and rimantadine, active against influenza A, and the neuraminidase inhibitors, zanamivir and oseltamivir, active against influenza A and B. In our experience, influenza B illness is as severe as influenza A. All agents have similar efficacy as treatment and prophylaxis against sensitive strains. When M(2) inhibitors are used simultaneously within an enclosed space (i.e. household or nursing home) as both treatment and prophylaxis, resistant strains may emerge that limit prophylactic efficacy. When M(2) inhibitors are administered to suspected cases (residents or staff) in institutions, precautions against secretion are especially important to diminish the risk of transmission of resistant virus. Rimantadine has been shown to have significantly fewer CNS adverse events compared with amantadine. Amantadine and oseltamivir require dosage adjustment in those with renal impairment. Oseltamivir, rimantadine and amantadine are administered by mouth, while zanamivir is administered by oral inhalation in a lactose powder. The labelling advises caution in the use of zanamivir in those with underlying airway disease. Pooled analysis of studies in patients given zanamivir indicate that individuals over the age of 50 years (at high risk for complications) and those severely symptomatic at presentation, tend to benefit most from early treatment. Neuraminidase inhibitors also diminish the need for antibacterials to treat secondary complications. An institutional programme to control influenza should include vaccination, and contingency plans for clinical surveillance, specimen processing and the rapid application of antiviral treatment and prophylaxis.

Delays in the application of outbreak control prophylaxis for influenza A in a nursing home

OBJECTIVE

To identify delayed prophylaxis from a pre-existing database and strategies to improve performance.

SETTING

A skilled nursing facility with 14 floors (4 buildings). The "outbreak unit" was a 50- to 60-bed floor.

METHODS

We performed surveillance during six seasons using one protocol. Prophylaxis was started when influenza was cultured in the building and 10% of residents on the floor had a new respiratory illness within 7 days. We defined delayed prophylaxis as four or more residents on a floor with positive cultures whose specimens had been collected within 5 days before the application of prophylaxis.

RESULTS

We identified 14 examples of delayed prophylaxis. In three, delayed prophylaxis was related to the 3.9-day delay between culture collection and culture report There was a high degree of commonality among building attack rates within a season. During six seasons, the first case in the last building occurred 27 to 64 days after the first case in the facility. The two seasons with the greatest activity (68 and 154 cases, respectively) began with explosive, multi-floor outbreaks in a single building. The match between the circulating strain and the vaccine was good, except in 1997-1998 when there were seven examples of delayed prophylaxis.

CONCLUSIONS

Influenza may involve buildings sequentially with a commonality of building attack rates. Explosive, multi-floor outbreaks early in the season could lead to a lower threshold for prophylaxis within a larger area when initial cases are encountered later in the season. This strategy could have prevented five examples of delayed prophylaxis. Rapid testing of multiple specimens while waiting for culture confirmation could have prevented three examples of delayed prophylaxis.