On 25 February, a businessman who had traveled to Hong Kong and Guangdong returned home to Taipei, marking the beginning of the outbreak on Taiwan. Almost all of those infected were either medical staff or family members of persons who had fallen ill. It is believed[by whom?] that the affected medical staff were unaware of the risks and were not using respiratory precautions such as masks, a safety protocol intended to protect medical workers from highly contagious diseases.