Remember, though, that these antiviral drugs are likely to reduce the duration of illness in otherwise normal influenza patients only if started within 2 days of fever onset, so the earlier we can intervene, the better. One study showed that starting oseltamivir within the first 12 hours of fever reduced illness by 3 days (41%) more than starting it at 48 hours of fever.
To be able to distinguish among the H1 and H3 influenza A strains, the most widely available tool is multiplex polymerase chain reaction. However, this can be expensive, ranging from $600 to $1,200 depending on the lab. Despite the conundrum posed by this year's A-strain divergent resistance, I don't think that these tests are worth the cost in outpatients. Consider such testing, however, in hospitalized patients or those at high risk for influenza complications, such as immunocompromised patients.
You can keep track of changes in influenza activity or resistance at www.cdc.gov/fluwww2a.cdc.gov/HAN/ArchiveSys/ViewMsgV.asp?AlertNum=00279