Q: If I contracted Chlamydia, did my wife cheat? I am 55 and have had only one sexual partner. We have been married for nearly 30 years. Could I have contracted chlamydia in any way other than sexually? My virility is flagging, so I don't blame my wife if she has gone elsewhere for sex; we have not had a successful sex life for many years. How can I broach this issue without upsetting her and damaging our relationship?

Suzi Godson

Chlamydia is not classified as a sexually transmitted infection for no reason. You don't catch it from toilet seats, kissing, sharing towels or taking a bite of someone else's Mars bar at the swimming pool. You do catch it from having unprotected penetrative sex. It is less commonly transmitted through oral and manual sex. Chlamydia is known as a “silent” disease because about three quarters of infected women and about half of infected men have no symptoms.

Although genito-urinary medicine (GUM) clinics advise those who have chlamydia to notify everyone they have had sex with in the past six months, it is thought that the bacteria can lurk undetected for years. There is a remote chance that you may have been tested and had a false positive result, but you can rule this out by doing another test. If you can't face the GUM again, you can buy reliable urine-based home-testing kits for £29.99 (drthom.com ), and if the result is positive, the treatment - a course of antibiotics - is free.

Men who leave chlamydia untreated can develop epididymitis, an infection in the tube that carries sperm from the testis, as well as sexually acquired reactive arthritis (SARA), a painful joint condition. Last year, research at Canalejo University Hospital, in Spain, suggested that chlamydia can also damage male fertility. It's the most common preventable cause of female infertility, as the infection causes the Fallopian tubes to become blocked. It can also cause lower abdominal pain.

Though you say you don't blame your wife for being unfaithful, if you risked an honest conversation with her, I suspect you'd find that she probably blames you. Married women are less opportunistic than men when it comes to infidelity. They stray because they feel unappreciated, unfulfilled and alienated from their husbands. Although you say, kindly, that you don't want to upset her or damage your relationship, in giving up on your sex life all those years ago, you may, inadvertently, have done both. If you think that you are being selfless in understanding that she might need to compensate for the lack of sex in your marriage by getting it elsewhere, think again. However well intentioned it might seem, to your wife of 30 years that sentiment translates into lack of interest. How much can you value her if you feel no anger at the thought of her making love to another man? And with so many treatments available for erectile dysfunction, can you see that your reluctance to do anything about your flagging virility smacks of lack of passion?

There is no diplomatic way of accusing your wife of being unfaithful and giving you an STI, but your wife will, undoubtedly, feel less threatened and find it easier to be honest if you own your part in the deterioration of your relationship. Strike a deal with her. If she wants to remain in the marriage and the affair is not historic, she must agree to end it immediately. In return, you must promise to make an appointment to see a doctor or a specialist in sexual dysfunction. Almost all cases of erectile dysfunction can be treated successfully; however, you and your wife will probably need the help of a sex therapist to re-establish sexual relations. Find a list of accredited therapists on the British Association for Sexual and Relationship Therapy website (basrt.org.uk ). Relationship counselling will also help. Relate (relate.org.uk ) provides face-to-face, online and telephone counselling and sex therapy. In London try Tavistock Centre for Couple Relationships (tccr.org.uk ).

Treating a dose of chlamydia is a picnic compared to addressing the complexities of a damaged relationship, but if you want your marriage to survive you need to do both.

- Suzi Godson is the author of The Sex Book (Cassell, £16.99)

Dr Mark Porter

Sexually-transmitted infections (STIs) should never be used as proof of infidelity, although they invariably are. In your wife's favour, most cases of chlamydia are symptomless and can lay latent and unrecognised for years (although 30 years would be pushing it).

If you have tested positive, your wife needs to be told so you can both be treated with antibiotics and screened for other STIs. This is not a time to be accusatory. Instead use it as an opportunity to talk about the problems in your relationship. It will give your wife the chance to come clean about past dalliances, and for you both to stop skirting around the issue of your flagging virility, by which I assume you mean that you are struggling to get a proper erection.

Impotence - or erectile dysfunction (ED) - is a relatively easy condition to treat. And it's not just your sex life and relationship that could benefit; ED is an important risk factor for heart disease and stroke. If the arteries supplying your penis are furred up, affecting your ability to get an erection, the arteries supplying your heart and brain are likely to be affected too.

Your GP will be able to prescribe the necessary antibiotics, do a few basic tests (blood pressure, cholesterol, etc) and discuss whether you are suitable for treatments such as Viagra. The rest is up to you and your wife.

- Mark Porter, GP, is the Times doctor

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