it is about the health of many people, or everybody, rather than one person. public health stops instead of encouraging a disease through surveillance of cases. to prevent being sick, it is good to act according to some simple advice: hand washing, regular check-ups, vaccination programmes, drinking clean water and using condoms. when infectious diseases break out, washing hands for about 30 seconds may be especially important. sometimes it is necessary to avoid masses of people or wear a surgical mask to protect yourself and to stop the spreading of the disease. teaching people how to live healthily and educate them, especially about sex and child-birth, is also very important.