Chlamydia is the most common sexually transmitted infection in the UK. Last year it accounted for almost half of all new STI diagnoses in England.

Key facts

  • In 2015, there were just over 200,000 diagnoses reported in England alone.
  • This represents a decline from 2014, of around 8,500. However this is thought to be due to a drop in testing coverage as opposed to fewer real cases.
  • The number of recorded diagnoses UK-wide peaked in 2011, with 236,595.
  • The infection is most prevalent among those in the 20-24 age range.
  • It is more commonly diagnosed in women than it is in men.

In this article, we’ll discuss chlamydia trends relating to:

  1. the UK
  2. Europe and the US
  3. age
  4. gender 
  5. and sexual orientation

Chlamydia in the UK

While the number of diagnoses for gonorrhoea and syphilis rose in England between 2014 and 2015, recorded chlamydia numbers actually fell from 208,638 to 200,288.

Public Health England notes that a drop from 99,785 diagnoses made in community-based settings to 93,036 was the main attributor to this fall. They also note that fewer heterosexual women were tested in such settings, and that this may have led to a drop in male partners being tested at sexual health clinics.

In England, chlamydia represented 46 percent of all new STI diagnoses in 2015.

UK-wide, the recorded number of cases saw a year-on-year rise between 2007 and 2011, where it reached a peak of 236,595. This number fell to 235,992 in 2012.

The Family Planning Association reports that in 2014 there were:

  • 16,320 new diagnoses in Scotland, 
  • 5,452 in Wales
  • and 1,868 in Northern Ireland.

Including the 208,638 cases in England, this brings the UK total for 2014 to 232,278, representing a further drop.

However, FPA also note that in England, in this decline may be due to a drop in testing. Among the 15-24 age group, they noted that in 2015, there was a drop of 9,500 diagnoses on the previous year, but 127,000 fewer tests taken.

Chlamydia in Europe and the US

According to figures from the European Centre for Disease Prevention and Control the UK recorded the highest number of chlamydia cases of any country in Europe for 10 consecutive years between 2003 and 2012.

In 2012, there were 385,683 total reported cases in the European Economic Area. With 235,992 cases, the UK accounted for 61 percent of these; however figures from Austria, the Czech Republic, Germany and Portugal were not included.

However, although the UK had the highest number of cases, it did not have the highest chlamydia prevalence per capita.

  • Iceland recorded the highest number of chlamydia diagnoses per 100,000 of the population in 2013, with 677.
  • Denmark had the second highest prevalence (461.2 per 100,000) and Norway the third highest (440.5 per 100,000).
  • The UK, by comparison, recorded 369.3 cases per 100,000.

Once again, this is discounting figures from the countries listed above whose data was not included.

The CDC reports that in the US in 2015, there were just over 1.5 million chlamydia diagnoses reported, which equates to 478.8 per 100,000. This represented an increase of 5.9 percent on the previous year, however the CDC speculate that the rise could be due to better screening coverage and more comprehensive reporting.

Globally, one study estimated that the number of female cases in 2012 was 68.5 million, and the number of male cases was 62.5 million.

Chlamydia in different age groups

In the UK and Europe, chlamydia is most common among young people, particularly the 20-24 age group.

Public Health England reported that in 2015 over 129,000, or 62 percent, of total chlamydia diagnoses were in the 15-24 age group.

The European Centre for Disease Prevention and Control reports that in 2013, the same age group accounted for 66.2 percent of chlamydia diagnoses in the European Economic Area, with 40.6 percent being among 20-24 year olds.

Generally, the 20-24 age group in most Western countries tends to be the most sexually active, and the most likely to engage in intercourse with casual or multiple partners. This is often cited as the reason behind higher STI diagnosis rates among younger people, however chlamydia infections in older age groups do occur.

Of the 383,793 European cases recorded in 2013, 93,713 (24.4 percent) were among 25-34 year olds and 22,189 (5.8 percent) were among 35-44 year olds.

Chlamydia by gender

Women are more often diagnosed with chlamydia than men in the UK and in several other European countries, as well as in the US.

According to the FPA, diagnosis rates among females in 2015 were:

  • 2,436.8 per 100,000 in the 15-19 age group
  • and 2,557 per 100,000 in the 20-24 age group.

Among males in the same year, rates were:

  • 824.4 per 100,000 in the 15-19 age group
  • and 1,693.8 per 100,000 in the 20-24 age group.

However the latest report by PHE* shows that in 2015, a higher percentage of male chlamydia tests were positive, which they stated was mostly due to higher testing rates among females.

In Europe, diagnosis rates in 2013 among females (of all ages) were 420.9 per 100,000, compared to 308.6 per 100,000 among males.

Diagnosis rates in the US in 2015 were higher among both sexes: 645.5 per 100,00 in women, and 305.2 per 100,000 in men.

Chlamydia by sexual orientation

Chlamydia is most common among heterosexual women and heterosexual men. European surveillance statistics from 2013 state that:

  • 91,289 cases were diagnosed in heterosexual women; 
  • 72,729 cases were diagnosed in heterosexual men;
  • and 12,376 were diagnosed in men who have sex with men.

the sexual orientation of 207,980 cases were recorded as ‘unknown’.

In England in 2015, 21 percent (12,805) of male chlamydia cases recorded in sexual health clinics were in men who have sex with men. This represents just six percent of the total number of chlamydia diagnoses.

You can read more about chlamydia on our information pages below. 

Page last reviewed:  Tuesday, Sep 05 2017