The number of people confirmed to have contracted Middle East Respiratory Syndrome, or MERS, increased to seven on Thursday, and the authorities said another person suspected of having the virus had left voluntary home quarantine to take a trip to China. The authorities said the two most recent confirmed cases involved people who are thought to have caught the virus from the person whose case was the first confirmed last week, a 68-year-old man who had traveled to Bahrain in April and May and then returned to South Korea via Qatar. “We should have checked more actively and broadly on family-related issues — we are deeply sorry about that,” said Yang Byung-kook, the director of the Korea Centers for Disease Control and Prevention. The health authorities have been criticized for not moving quickly and effectively enough to quarantine suspected patients.