In the eighteenth and nineteenth centuries congenital syphilis was a major cause of infant mortality in France but mercury, the preferred treatment for the disease, could not be safely given to infants. In the 1780s the Vaugirard hospital in Paris began to treat affected infants by giving mercury to wet nurses, who transmitted it to infants through their milk. Despite the highly contagious nature of syphilis and the dangerous side-effects of mercury, the practice of using healthy wet nurses to treat syphilitic infants spread throughout France and continued into the nineteenth century.

Infection of the Innocents describes the pioneering experiments at the Vaugirard in the 1780s and tells the stories of healthy women who contracted syphilis by nursing infants in the nineteenth century. It explores the legal cases that wet nurses brought against the doctors and families whose secrecy about the infant's health had exposed them to the debilitating disease. One of the key findings is that some women actually won damage suits against doctors and families, leading to reform of the law governing doctor-patient confidentiality.