NEARLY 20 years ago, the Centres for Disease Control and Prevention (CDC) released an ambitious proposal to “eliminate syphilis from the United States”. The plan seems to have worked rather poorly. Soon after the proposal’s issue, infection rates began to head in the wrong direction and then worsened. From 2000 until 2016, the most recent year for which data are available, the rates of syphilis quadrupled. Congenital syphilis, a nearly eradicated condition in which the infection is passed from mother to fetus, has also sharply increased—by nearly 28% from a low base in one year. That is distressing not only because the disease is easily detected and treated by a course of antibiotics, but also because afflicted mothers have a 40% chance of a stillbirth.

The problem is not only limited to syphilis. Other sexually transmitted diseases (STDs) are roaring back. Rates of gonorrhoea have, after a brief period of decline, surged 46% since 2010. Chlamydia, an extremely common STD which can result in female infertility, has nearly doubled since 2000. Nearly every sort of American has been affected. Even though people under 30 account for a large share of new infections, STDs have also risen among the elderly. Among adults aged 55 or over, chlamydia has more than doubled since 2010, while gonorrhoea has more than tripled. The public-health departments of New York City and Los Angeles County have sounded alarms, as have rural states like Mississippi, where STD rates are among the highest in the country.

The way STDs are spread—through unprotected sex with the infected—is no real mystery, even to those adolescents brought up in the most wholesome settings. So what accounts for the rise in transmission? A few theories exist. The first lays the blame on dwindling public dollars for STD prevention and monitoring programmes. Since 2003, the CDC’s STD prevention budget, which funds state health departments and clinics, has declined by 40% in real terms. The funding slide continued through presidencies of both parties, although the Trump administration pitched a 17% cut to the programme last year (and a 19% reduction to the CDC’s HIV prevention programme to boot). Clinics offering confidential services are especially important for young people, who often do not seek testing through their general practitioners “both because of stigma, and because doctors do not really like to talk about sex”, says David Harvey, the executive director of the National Coalition of STD Directors, an advocacy group.

Another explanation is that sex is now seen as less risky. The most widely feared venereal disease, HIV, is much less scary than it once was. Gay and bisexual men, who are still at extremely high risk of HIV infection in America, are now encouraged to take prophylactic pills once a day that can reduce the chance of infection by 99%. For those who contract HIV, antiretroviral medicines offer the chance of a near-normal life. But the pills do not shield gay men from other STDs. They have accounted for a mightily disproportionate share of the newly infected.