Genital herpes simplex infection
In 2002, 940 infections were isolated; this figure compares with 1033 in 2001 and annual averages of 955 for 1999-2002, 791 for 1995-1998 and 666 for 1992-1994 (Table 1). Between the early and late 1990s, almost all of the increase in herpes simplex incidence was due to rising rates among women. In 2002, 26% of infections were isolated from persons aged under 25 years; the corresponding rate for 1992 was 31%.

Table 1. Genital herpes simplex, Scotland 1992-2002: laboratory isolates by gender and age group. Source: SCIEH.

*Includes cases where gender is not known

Genital chlamydia
In 2002, 12 392 isolates were reported to SCIEH, a 16% increase on the previous year’s total (10 636), and a 62% increase on that recorded for 2000 (7654) (Table 2). As with genital herpes simplex infection, the gender distribution favours women; in 2002, they represented 71% of all infections isolated. Genital chlamydia is an infection which predominates in young people; in 2002, 52% of all infections were isolated from persons under the age of 25. The dramatic increase in the incidence of genital chlamydia diagnoses throughout Scotland over the last decade is demonstrated by comparing rates for 1992 with those for 2002 (Figure).

Table 2. Genital chlamydia infection, Scotland 1992-2002: laboratory isolates by gender and age group. Source: SCIEH.

*Includes cases where gender is not known

Figure. Genital chlamydia infection, Scotland 1992-2002: laboratory isolates by gender and age group. Source: SCIEH.

Gonorrhoea
In 2002, 821 episodes of gonorrhoea were reported to SCIEH; this figure compares with 817 in 2001 and annual averages of 217 for 2000-2002, 139 for 1995-1999, and 172 for 1992-1994 (Table 3). Unlike for genital herpes simplex and genital chlamydia infections, the majority of cases are in men. The annual average number of male cases increased by 219% from 278 in 1992-1994 to 609 in 2000-2002; the corresponding increase among women was 25% (172 to 216). The considerable increase in gonorrhoea among men, seen in the late 1990s, is considered to be largely due to transmission among men who have sex with men (MSM). This is corroborated by the increase in rectal isolates of gonorrhoea from 34 in 1999 to 54 in 2000, 53 in 2001 and 78 in 2002 (2). In 2002, 67% of episodes of infection among women occurred in those under 25 years; the corresponding rate for men was 35%.

Table 3. Gonorrhoea, Scotland 1992-2002: laboratory reports (episodes) by gender and age group. Source: SCIEH.

*Includes cases where gender is not known. One episode of gonorrhoea corresponds to an infected individual from whom more than one isolate could have been recovered.

Conclusion
Infections among heterosexuals
Because laboratory reports contain no information about sexual orientation, it is impossible to know whether infections in males are occurring within a certain group, for example heterosexuals, or MSM. Analysis of STI rates among women provides the best gauge of infection among heterosexual populations as a whole. Trends in herpes simplex and gonorrhoea among women should be considered true reflections of any changes in high risk sexual behaviour among heterosexual populations. Evidence suggests that there has been a modest increase in STIs among heterosexuals in Scotland in recent years.

The interpretation of trend data for genital chlamydia is difficult because chlamydia is often an asymptomatic infection, which is diagnosed through screening. Accordingly, increases in the numbers of genital chlamydia diagnoses are as likely to be due to changes in screening practice as to increases in the incidence of infection. Although it is not known whether the incidence of genital chlamydia infection has increased in recent years, there is no doubt that very large numbers of people, young adults in particular, are infected. Such data indicate that casual unprotected sexual intercourse among young heterosexuals remains a major problem in Scotland.

Infections among MSM
For MSM, the increase in rectal gonorrhoea is worrying and is consistent with the recent increase in the incidence of syphilis in this population. In 2002, there were 31 cases of syphilis among gay men, mainly in Edinburgh and Glasgow. These observations are of great concern as gay men are at high risk of acquiring HIV infection.

Acknowledgements
SCIEH wishes to thank Joan McElhinney at the SNGRL for help with database maintenance and analysis, as well as the Consultant Microbiologists and their staff who supply data to the SNGRL and SCIEH.