Sexually Transmissible Infections in Clinical Practice

1. A Man Requesting a Sexual Health Screen

Alexander McMillan1, 2  


Department of Genitourinary Medicine, NHS Lothian, Edinburgh Royal Infirmary, Edinburgh, Uk


University of Edinburgh, Edinburgh, Uk

Alexander McMillanFormerly, Consultant Physician, part-time Senior Lecturer



A specific history should be taken to elicit any symptoms that the individual may not have recognized as being those of a sexually transmissible infection (STI). (It is usually helpful to elicit this history before enquiring about sexual activity: it helps to establish rapport with the patient before questioning about intimate activities). For example

Robert, a 23-year-old student, attends a Sexual Health clinic and requests testing for sexually transmissible infections (STIs).

1.1 What History Would You Obtain from Robert?

A specific history should be taken to elicit any symptoms that the individual may not have recognized as being those of a sexually transmissible infection (STI). (It is usually helpful to elicit this history before enquiring about sexual activity: it helps to establish rapport with the patient before questioning about intimate activities). For example,

·               Has he had discomfort on passing urine?

·                                   If so, consider urethritis.

·               Has he noticed “growths” on the genitalia?

·                                   If so, consider genital warts, molluscum contagiosum, or normal anatomical variants, such as coronal papillae.

·               Has he had an itch in the skin of the pubic area, genitocrural folds, shaft of the penis, scrotum, buttocks, or perianal region?

·                                   If so, consider phthiriasis and scabies, in addition to non-STI causes such as tinea cruris.

·               Has he noticed swollen lymph glands in the groin (Fig. 1.1) or elsewhere in his body?

·                                   For example, painless inguinal lymph node enlargement may be a feature of primary syphilis and generalized lymphadenopathy may be associated with secondary syphilis or HIV infection.

·               Has he had testicular pain or discomfort? Some men with urethral chlamydial infection complain of testicular discomfort in the absence of frank epididymo-orchitis.


Figure 1.1.

Bilateral inguinal lymph node enlargement in primary syphilis.

The taking of an accurate sexual history is important so that the most appropriate microbiological tests can be undertaken and the need for any subsequent investigations. The following information should be obtained:

·               The date of his most recent sexual contact, and, if penetrative sex had been performed, were condoms used? (Remember the pre-patent periods of the STIs, e.g., gonococcal urethritis between 1 and 10 days and chlamydial urethritis 7–21 days. Note: Testing for STIs in the symptomless patient is generally deferred until 7–10 days after the most recent sexual risk.)

·               Does he have a regular sexual partner, and, if so, for how long have they been in the relationship, and when did he last have sex with his partner? (Remember that one person’s definition of “regular” may differ significantly from that of another!)

·               If he has had sexual contact within the preceding 3 months:

·                                   How many different partners has he had?

·                                   What were the approximate dates of these sexual contacts? Again this is a relevant question with respect to the pre-patent periods of the infections.

·                                   What was the gender of these partners? Remember that a sizeable proportion of men who are predominantly heterosexual have had homosexual contact. If he has had homosexual contact, it is helpful to enquire about what sexual activities had occurred (see Case 4). This will inform on possible risks of infection with, for example, HIV and syphilis.

·               How many lifetime sexual partners has he had:

·                                   What was the gender of his partners?

·                                   Has he always used condoms for vaginal, anal, or oral–genital sex? Consistent use of condoms reduces the risk of infection with some, but not all, STIs. Examples of the former include gonorrhoea, chlamydia, and syphilis, and an example of the latter, human papillomavirus.

·                                   What was the country (countries) of origin of his sexual partner(s)? This is particularly important when considering the risk of infection with HIV, hepatitis B virus, and syphilis, conditions that are more prevalent in geographical areas outwith Western Europe, Australasia, and the United States of America.

·               Has he had any STI in the past, and if so what, and when? This history is particularly important in the interpretation of positive serological tests for syphilis (see Cases 1819, and 33).

·               Has he ever been tested for HIV, and if so when, and what was the result?

·               Has he or any of his sexual partners ever injected recreational drugs? If so, it is important to note when that (these) risk(s) occurred because of the often long pre-patent period before serological tests for the blood-borne viruses become positive.

·               Has he had any serious medical conditions in the past, and what is the current state of his general health?

·               Is he currently receiving medication, and if so what? This is important to know because of possible drug interactions with any drugs used for the treatment of STIs.

·               Has he taken any antimicrobial drugs within the preceding month? Such therapy may have inadvertently treated an STI.

·               Has he ever had a hypersensitivity reaction to drugs, particularly to antimicrobial agents?

Robert has no symptoms suggestive of the presence of an STI. The reason for his clinic attendance is that he has met a young woman with whom he wishes to form a relationship, and does not wish to infect her with an STI of which he is unaware. His most recent sexual contact had been 3 weeks previously with an ex-girlfriend, with whom he had been in a relationship for 3 months. He used a condom for vaginal intercourse but not for oro-genital sex. He has had no other sexual contacts in the preceding 3 months. Each of his six lifetime sexual partners was female, and there is no history of homosexual contact. Each partner was from the United Kingdom. Although he is aware of the risk of acquisition of STI from unprotected sex, he has not used condoms consistently. He has smoked cannabis in the past, but has never injected recreational drugs. He is not aware of injecting drug use by any of his sexual partners. His general health is good, and he is not currently receiving any medication. There is no history of antimicrobial drug use in the preceding month. He has no known drug allergies. He has not been vaccinated against either hepatitis A or B.

1.2 Outline the Physical Examination You Would Perform and Indicate Which Microbiological Tests You Would Undertake in This Case

The extent of the physical examination will be determined by the history. As Robert has no history of a rash or swollen lymph nodes, it is reasonable to confine the physical examination to the anogenital area. This examination is best performed with the patient lying on a couch in a warm and well-lit room. He should be offered a chaperone with whose gender he feels comfortable.

As up to 90% of men with uncomplicated chlamydial infection are symptomless, it is imperative that at least this infection is specifically looked for when a patient requests an STI screen. As gonococcal infection of the urethra is symptomless in up to 5% of cases, tests for Neisseria gonorrhoeae should be undertaken. Untreated, both infections have serious sequelae (see Cases 13 and 24).












Physical examination has failed to identify features of any STI; a urine sample is sent for the detection of N. gonorrhoeae and C. trachomatis. Robert accepts the offer of serological tests for syphilis and HIV. He is asked to contact the clinic for the results of the laboratory tests 1 week later.

At this time he contacts a Health Adviser. He is told that the test results are negative and that there was no evidence on infection. Robert, however, is uncertain as to the accuracy of the tests. What information would you provide?

Robert is assured that the tests for gonorrhoea and chlamydial infection are reliable. The sensitivity of NAATs is superior to culture for the diagnosis of urethral gonorrhoea in men. Although the sensitivity and specificity2 2 of polymerase chain reactions (PCRs) for N. gonorrhoeae are reported to be about 90 and 99.5%, respectively, for urine samples, the sensitivity is somewhat lower in symptomless than in symptomatic men. Slightly higher sensitivity (about 96%) is reported when urethral swabs are used as specimens.

The sensitivity and specificity of PCRs for C. trachomatis are about 84 and 99%, respectively, for urine samples. The sensitivity compares well with that of about 88% for urethral swabs.

As the sensitivity, specificity, positive-predictive, and negative-predictive values of NAATs for the diagnosis of infection using a first-voided specimen of urine are similar to those using directly obtained urethral material and does not involve invasive sampling, this specimen is preferred for screening.

As his most recent sexual contact had been only 3 weeks before testing, and the pre-patent period of syphilis varies between 10 and 90 days, Robert should be offered repeat testing in about 8 weeks time if he is concerned. In this case the risk of syphilis is low (most cases of syphilis in the United Kingdom have been acquired through homosexual contact or from individuals who have traveled from geographical areas where the infection is prevalent), and it is probably unnecessary to insist on repeat testing.

As HIV antibodies may take up to 3 months from infection to become detectable, a negative test at this time cannot exclude infection. Robert should be offered re-testing in about 8 weeks time, although, as in the case of syphilis, the risk of HIV infection is low (most cases of HIV infection in the United Kingdom have been acquired through homosexual contact, from unprotected vaginal or anal sex with a person from a geographical area where HIV is prevalent, or from sharing contaminated equipment used for injecting recreational drugs).

Robert has read about inapparent genital herpes and asks why he has not been tested for this viral infection. He has never been aware of any genital or oral lesions suggestive of genital or oral herpes, and none of his sexual partners is known to have genital herpes. What would you tell Robert?

Robert is correct in his understanding that many cases of genital herpes are symptomless. Only between 10 and 25% of individuals with serological evidence of herpes simplex virus (HSV) type 2 infection are aware that they have genital herpes (worldwide, HSV type 2 is the most common type associated with genital infection). In the absence of clinical lesions that can be sampled for virological testing (see Case 16), serology remains the only means for detecting infection. Type-specific glycoprotein G (gG)-based assays are available that have sensitivities for the detection of HSV-2 antibodies of between 80 and 98% and specificities greater than 96%. The positive-predictive value (see Note 2), however, is poor in low prevalence populations. There is a good correlation between the seroprevalence of HSV type 2 and increasing age, the number of years of sexual activity, and the number of sexual partners. As Robert is young, has been sexually active for a short period of time, and has had few sexual partners, a positive result from his serum does not necessarily reflect true infection.

In some industrialized countries, including the United Kingdom, almost 50 and 70% of new genital herpes infections are associated with HSV type 1, the viral type classically associated with orolabial herpes. As in the case of genital infection with HSV type 2, more than one-third of orolabial infections are symptomless. In the absence of a history of oral or genital lesions it is therefore impossible to tell whether the detection of HSV type 1 antibodies reflects orolabial or genital herpes.

Opinion is divided as to whether or not HSV type-specific serology should be part of a sexual health screen. On the one hand, infection is lifelong, there is no curative treatment, and the psychological morbidity associated with a diagnosis of HSV type 2 infection can be profound. On the other hand, however, seropositive individuals can be taught to recognize minor recurrences and avoid intercourse at that time, thereby reducing, but not eliminating, the risk of transmission to a partner. With adequate support, the psychological impact is usually short lived. Persons with HSV type 1 antibodies should be advised to avoid oral–genital sex with a partner who has no history of orolabial herpes, or who is not known to be seropositive for that viral infection.

After this discussion, Robert does not wish to be tested for type-specific HSV antibodies.



A positive result in a nucleic acid amplification assay should preferably be confirmed by culture or an alternative NAAT.


True Positive


False Positive


False negative


True negative


Sensitivity = w/(w+y). Specificity = z/(x+z)

Positive predictive value = w/(w+x). Negative predictive value = z/(y+z)