At least four ex-patients of a Canadian doctor accused of failing to follow infection prevention protocol have tested positive for hepatitis C, a law firm says.The Merchant Law Group has filed a class-action suit against Dr. Christiane Farazli on behalf of two former patients, the Canadian Broadcasting Corp. reported Wednesday. Nicholas Robinson, a lawyer with the firm, said all four are current or former residents of Ottawa who were treated at Farazli\'s clinic in the city.Ottawa Public Health sent letters to patients treated at Farazli\'s clinic between 2002 and June 2011 after starting an investigation into her procedures. In a memo to the city council and the Ottawa board of health, Dr. Isra Levy said at least 3,400 former patients, about half of those who received letters, have already been tested.Levy told CBC that in a group that large some people are almost certain to test positive for hepatitis C, hepatitis B and the HIV virus. While the viruses can be spread by unclean medical instruments, they are not unusual in the general population.