The Rapid Service Laboratory offers a rapid assay for the diagnosis of Influenza A and B. Call Ext. 8044 to obtain the special swabs needed for nasopharyngeal or throat sampling. If alerted ahead of time, reagents can be warmed, the results should be available within 30 minutes. Once influenza is established in the community, individual testing is generally not needed; during an outbreak, most compatible viral infections are likely to be influenza.
The neuraminidase inhibitors selectively inhibit both influenza A and B. Current drugs are zanamivir (Relenza-inhaled) and oseltamivir (Tamiflu-oral). These drugs offer effective treatment of influenza A or B if started within 24-48 hours of onset of disease. For ease of use, many prefer oseltamivir at 75mg b.i.d. for 5 days (just once a day if the creatinine clearance is less than 30ml/min). While expensive, these drugs are effective also for prevention (although only oseltamivir is FDA approved for prophylaxis). For oseltamivir at 75mg q.d. for 6 weeks, there was 76% effectiveness in wells, and 92% in a frail, elderly, residential home setting. Similar results were seen with a one-week course of oseltamivir or a 10-day course of b.i.d. zanamivir family member prophylaxis.
Also useful for treatment of active infection with influenza A (the strain that typically causes the winter outbreak in adults) is amantadine or the more expensive but better tolerated rimantadine. Adjust the dose for diminished renal function. For both drugs the usual dose is 100mg b.i.d. For patients 65 or older, the amantadine dose is reduced to 100mg q.d., and even less in renal failure. This same reduced dose is used for rimantadine in elderly nursing home patients or those with renal or hepatic dysfunction. These drugs also have been used for prophylaxis, in the midst of an outbreak, especially in patients unable to be immunized. Resistance development has been noted in one-third of treatment courses and when used widely in a nursing home setting.