A new study by researchers in the UK has found an alarming rate of the bacterial infection Mycoplasma genitalium (MG), a suspected but unconfirmed sexually transmitted infection (STI) among the sexually active general population in Britain.

Compared to some other STIs, MG is relatively hard to detect as the infection doesn't present many symptoms, meaning many who are affected are not aware that they're carrying the bacteria.

However, a urine analysis taken from 4,500 participants in Britain's third National Survey of Sexual Attitudes and Lifestyles has revealed that as much as 1 percent of the population aged 16–44 who have had at least one sexual partner are infected with MG – likely more than 200,000 people.

While MG is not yet officially considered an STI, this new research may provide further evidence that it should be treated as such, as the infection rates in the study suggest prevalence is greater among people who have higher levels of sexual activity.

Specifically, prevalence was markedly higher in people who reported more than four sexual partners in the past year, with 5.2 percent and 3.1 percent of such men and women affected respectively. Further, the researchers say that the absence of the infection in more than 200 16- to 17-year-old virgins who took part in the study is evidence that MG is transmitted sexually.

The 25–44 year age group is the most likely to be affected by MG, with more than 90 percent of MG infections in men and more than two-thirds in women occurring in that bracket. The most likely people to test positive for MG are those with risky sexual behaviours, men of black ethnicity, and those living in poorer areas.

While not much is known about the long-term outcomes of MG, it's believed to play a role in pelvic inflammatory disease, infertility and ectopic pregnancy.

The findings, published in the International Journal of Epidemiology, are hoped to raise awareness of the infection, especially since so few who carry it show symptoms: more than 90 percent of infected men and over half infected women in the study did not show any symptoms.

"These findings suggest that only testing those who are currently symptomatic would miss the majority of infections," said Pam Sonnenberg, an epidemiologist at University College London and lead author of the paper. "However, further research is needed to understand the clinical implications of infection and possible longer-term complications."