Low incidence of rimantadine resistance in field isolates of influenza A viruses

The spread of drug-resistant influenza viruses type A to close contacts in families, schools, and nursing homes has been well documented. To investiga te whether drug-resistant influenza viruses circulate in the general popula tion, 2017 isolates collected in 43 countries and territories during a 4-ye ar period were tested for drug susceptibility in a bioassay. Drug resistanc e was confirmed by detection of specific mutations on the M2 gene that have been shown to confer resistance to amantadine or rimantadine. Sixteen viru ses (0.8%) were found to be drug-resistant, Only 2 of these resistant virus es were isolated from individuals who received amantadine or rimantadine tr eatment at the time the specimens were collected. For 12 individuals use of amantadine or rimantadine could be excluded, and from the remaining 2 pati ents information about medication was unavailable. These results indicate t hat the circulation of drug-resistant influenza viruses is a rare event, bu t surveillance for drug resistance should be continued.