Syphilis is on a steep rise throughout the US, but a few cities are seeing particularly unprecedented rates.

The STD is wreaking particular havoc in California and a series of hot spots across the nation.

In San Joaquin, the rate of syphilis cases in 2017 was 50.9 per 100,000 - a 44 percent increase over the previous year.

Parts of Palm Springs in southern California saw as many as 185 cases of syphilis per 100,000 people.

It isn't just California, though: rates of the infection are 300 percent higher than they were a decade ago and Milwaukee has a 'cluster' of 125 people with syphilis.

Syphilis is a nationwide issue, and experts worry that HIV treatment triumphs have actually created a false sense of sexual safety, leading to higher rates of unprotected sex - especially among men who have sex with men, who have the highest incidence of syphilis, too.

In February 2018, the AIDS Healthcare Foundation unveiled a billboard warning of the dangers of syphilis in Los Angeles, where syphilis is up 16 percent and the congenital form of the disease that affects and can kill babies surged by more than 60 percent in 2016

Sexually transmitted syphilis is unpleasant and can become dangerous if it's left untreated, but with proper, early medical attention, the infection is easily curable.

But if it passes to a developing baby through an infected woman's placenta, the disease can cause serious birth defects and even lead to stillbirth.

High rates of syphilis in any population are a public health concerns, but 'when we start seeing it in babies, that should set off alarm bells,' says Dr Cameron Kaiser, health officer at the Riverside County Health Department.

'We have built up such a reservoir of cases [of sexually transmitted syphilis] that it's started to leak over into our pregnant population.

'The numbers are still double digit, but when we see these cases rise, that the terminal state.'

Syphilis is typically most common among men who have sex with men - and that has been the case in Riverside, San Joaquin and other locations with high rates of the disease.

'The rise is a nationwide trend,' says Dr Kaiser, 'but I think for many places it does track vulnerable populations like men who have sex with men, but we're seeing it in babies too, so it has to be in the heterosexual populations too.'

Sadly, the advent of effective preventative drugs and treatment for HIV may have created a window of opportunity for the spread of syphilis between men who have sex with men.

WHAT IS SYPHILIS? Syphilis is a bacterial infection that is usually caught by having sex with an infected person. It spreads through close contact with an infected sore, which usually happens during vaginal, oral or anal sex. Infected pregnant women can pass the STI to their unborn babies, which can lead to miscarriages or stillbirths. Syphilis can also be spread by sharing needles with an infected person. Symptoms are not always obvious and may eventually disappear. These could include: Small, painless sores or ulcers on the penis, vagina, anus or around the mouth

Blotchy red rashes on the palms or soles of the feet

Small skin growths on women's vulvas or the anus

White patches in the mouth

Fatigue, headaches, joint pain, fever and swollen lymph nodes If untreated, syphilis can spread to the brain or elsewhere in the body and cause disabilities or death. Treatment is usually an antibiotic injection into the buttocks or a course of tablets. People can reduce their risk by using condoms during sex, a dental dam (plastic square) in oral sex and avoiding sharing sex toys. Source: NHS Choices Advertisement

'What we've heard at community meetings is that a lot of people had this imperative about safer sex during the 1980s. Everyone was very concerned abut HIV ... but that imperative isn't there because it's so much more treatable,' says Dr Kaiser.

'People think: "Why should we use a condom? We can get treated."'

But preventive medications like PrEP and treatments for HIV do nothing to prevent the transmission of syphilis, or any other sexually transmitted diseases.

The only thing that may protect someone from getting infected if their partner has syphilis is a condom - which is highly, but not perfectly, effective.

'We're starting to lost the battle with syphilis, chlamydia and gonorrhea,' says Dr Kaiser.

In 2017, rates of syphilis gonorrhea and chlamydia in the US hit a record high for the fourth year in a row, according to the latest data from the Centers for Disease Control and Prevention.

In 2015, the national average rate of syphilis cases was eight per 100,000 - four times the record low.

In Palm Springs, which has been dubbed by some a 'gay mecca,' there were more than 100 cases per 100,000 people in 2017 - 10 times the latest national average.

But Dr Kaiser notes that the syphilis problem isn't just a hyper-local one. In fact, that's part of the problem.

'We get a lot of snow bird traffic, especially in Palm Springs, over the winter,' he says.

'This is going to require a regional solution because it's a regional issue.'

Syphilis is becoming a national concern as well, but it is intersecting regional populations that are infecting one another.

In the wake of the discovery of a 'syphilis cluster' of 125 people in Milwaukee, Wisconsin, diagnosed around the same earlier this year, a Forbes article warned that it wasn't just alarming for Milwaukee, but for surrounding areas.

Part of the reason for this concern is that STDs still go far under-reported and under-diagnosed. The less record of a case of syphilis there is, the more likely that that person won't tell partners and will pass along the infection.

Alongside the Riverside County Syphilis Community Collaborative, which had its first meeting in May, Dr Kaiser is trying to improve partner monitoring, among other initiatives.

'We're working with medical providers and hospitals trying to figure out the barriers to people getting tested and treated,' he says.

'We want to expand the ability of medical providers to do partner treatment. If you have one case, you have to have a second.'