EPIDEMIOLOGY, which encompasses both the systematic study of infectious disease and the implementation of the means to contain it, is something of a medical oddity. As dependent on statisticians and politicians as it is on medical-care providers, and often used at times of desperation, by practitioners who have been accorded police and in certain cases military powers, epidemiology has sometimes had to strike a balance between the harshness that may be required to control infectious diseases and the civil liberties of people whose rights may be subject to abridgment.
Since the turn of the century, with the introduction in this country of bacteriological testing and the establishment of boards of health, standard public-health measures have been deployed against infectious diseases. These measures, leaving aside the extreme step of holding people in quarantine, have typically included at least some of the following: routine testing for infection, often undertaken without explicit patient consent; reporting to local health authorities of the names of those who test positive for infection; contact tracing, or the identification of any people who may have been exposed to infection; and notification of these possibly infected people that they may have been exposed. Some combination of these four practices has been commonly applied against outbreaks of infectious diseases, including typhoid, diphtheria, and tuberculosis, and against upsurges in sexually transmitted diseases. It would be surprising if, out of all the viruses and bacteria that can do us significant harm, one was exempted from the scope of these measures. It would be even more surprising if the one chosen pathogen was responsible for an epidemic that today constitutes the leading cause of death among all Americans aged twenty-five to forty-four.