A strain of influenza virus resistant to the antiviral drug Tamiflu was found in a total of five flu patients in Yokohama city with three of them believed to comprise a case of group infection, health officials of the city said Thursday. Relenza, another antiviral drug, was effective for the patients, who were all infected with the type A Soviet Union flu. The Yokohama City Institute of Health advised caution in selecting a drug for that type of influenza. The five were residents aged 8 to 13 of the same ward in Yokohama who saw doctors on Jan 28. Three were students at the same elementary school, while the other two were diagnosed at the same health care institution.