Advances in the diagnosis of sexually transmitted diseases caused by bacteria

Chlamydia: once detected, easily overcome

A disease of men and women that starts with a mild burning sensation on passing urine can often progress to painful inflammation of the urethra or fallopian tubes and ultimately to permanent sterility. The cause is an in most cases sexually transmitted infection that is acquired by three to four million people per year in Europe and the USA alone. This disease is problematic not so much in terms of its treatment - effective antibiotics are available - as in terms of how to achieve prompt identification of the causative organism, Chlamydia. This is because in around three quarters of affected women and a quarter of affected men the infection is virtually asymptomatic in its early stages.

1. Inflammation in adults and a risk to neonates

Chlamydial infections are among the most common sexually transmitted bacterial diseases of humans, and are estimated to be about 40 times more common than syphilitic infections throughout the world. If not treated they can lead to sterility. Even if there are no symptoms initially, epididymitis can develop later. Half of all cases of urethritis are due to chlamydia.

In Europe around a million women per year are diagnosed as having salpingitis, and around 600,000 of these infections are due to Chlamydia trachomatis. Roughly one female patient in five becomes infertile as a result of adhesions in the fallopian tubes. Of a million women in the USA with pelvic inflammatory disease, 40 percent were found to have C. trachomatis infection.

Chlamydial infection commonly causes mucopurulent cervicitis, urethritis, or infection of Bartholin's glands (two small glands that lie on either side of the entrance to the vagina).

Pregnant women with chlamydial infection have a considerably increased incidence of tubal or abdominal pregnancy and premature delivery. Uterine bleeding and need for hysterectomy can occur as late sequelae. Even neonates of infected mothers are not spared, chlamydiae being responsible for around 10,000 cases of neonatal pneumonia and conjunctivitis per year.

Although symptoms such as urinary burning (scalding), vaginal itch and discharge, intermenstrual bleeding, and lower abdominal pain with fever may alert some women to the presence of chlamydial infection, many women experience no symptoms at all initially. Similarly, a quarter of male patients experience no symptoms for a long time after infection.

Once identified, the infection can be treated relatively simply, and in most cases successfully, with antibiotics. Nevertheless, most patients who experience no symptoms don't go to see a doctor in the first place.

2. Precise diagnosis is essential

Early diagnosis can prevent serious complications. Methods of identifying chlamydial infection include cultivation of the organism, enzyme immunoassay, fluorescent antibody tests, and the polymerase chain reaction (PCR).

Each of these techniques has advantages and disadvantages in terms of specificity and sensitivity, and this must be borne in mind in the interpretation of test results. One critical factor is the sensitivity of detection of chlamydia. False-negative results allow the disease to spread further and delay the start of treatment, making subsequent complications more likely. False-positive results cause unnecessary psychological suffering and lead to unnecessary treatment.

Although cultivation of the organism is the "gold standard" of diagnosis, the sensitivity of culture-based methods is only about 80 to 90 percent. They are labour-intensive, take three to five days to yield a result, and are therefore relatively expensive.

Tests that take advantage of the high sensitivity of the PCR technique in terms of identifying bacterial diseases are gradually becoming established in regular laboratory practice.

3. Rapid results with the PCR method

As the PCR method requires only a single DNA segment from the bacterial genome, a minute sample of material is sufficient for the demonstration of chlamydia. The characteristic DNA segment is first separated into its individual strands. Each of these is then joined to a synthetic oligonucleotide sequence to form a double strand. This process of amplification is repeated until the amount of the desired DNA is adequate for the purpose of identification.

The AMPLICORTM test for chlamydiae yields extremely precise results within about four hours. It thus provides accuracy of diagnosis and permits specific treatment. Another advantage of this method is that unlike tests based on cultivation of the organism, it can detect chlamydia even in the urine of infected men. It therefore dispenses with the need for urethral swabbing, an unpleasant and sometimes painful procedure. In the case of women a cervical swab, or likewise a urine sample, is generally taken.

Though chlamydial infection is up to ten times more common than gonorrhea ("the clap"), scientists in the USA have found that in the past few years increasing numbers of patients with chlamydial infection also have gonococcal infection. For this reason a test kit (AMPLICORTM CT/NG) that can detect not only Chlamydia trachomatis (CT), but also Neisseria gonorrhoeae (NG; gonococci), is also supplied.

The signs and symptoms of these two infections are in fact very similar, except that in the case of chlamydia they occur later and less abruptly and are generally less severe. The incubation period of C. trachomatis infection is generally one to three weeks, whereas that of gonorrhea is a few days.

4. Conjunctivitis as a cause of blindness

Chlamydiae have been known for many years to be responsible for various diseases in humans. On the basis of certain biochemical characteristics, they have now been classified as bacteria rather than viruses. Their growth and replication is dependent upon the metabolism of suitable host cells. For this reason they can also be described as "cellular energy parasites".

Chlamydia trachomatis causes not just the sexually transmitted disease described above, but also trachoma (granular conjunctivitis, Egyptian ophthalmia). This chronic form of conjunctivitis is still one of the commonest causes of blindness, as evidenced by the fact that approximately 20 million children and adults are affected worldwide. The pathogen is transmitted by direct contact from human to human, via contaminated objects, or via polluted water.

Inclusion conjunctivitis is an acute inflammation of the eye that arises from a primary chlamydial infection of the urogenital tract.

Lymphogranuloma venereum is another sexually transmitted chlamydial infection. This disease manifests itself as painful inflammation of the inguinal lymph nodes. It occurs mostly in tropical countries and is very rare in Germany.

Chlamydia psittaci is the pathogen of ornithosis (psittacosis, parrot fever), an acute infectious disease transmitted to humans by parakeets, parrots, pigeons, seabirds, ducks, and geese. The pathogens can be found in the blood, tissues, feathers, and feces of infected birds. After entering the human body by penetrating the mucous membranes of the upper airways, they cause fever and pneumonia.

5. Are chlamydiae responsible for myocardial infarction?

Chlamydia pneumoniae, an organism identified as a pathogen only a few years ago, has recently received a great deal of attention from the media because it is suspected of contributing significantly to the development of atherosclerotic plaques and thus increasing the likelihood of occurrence of myocardial infarction. This is because this chlamydial species is very commonly found in these deposits on the internal lining of blood vessels.

C. pneumoniae causes a generally mild form of atypical pneumonia characterised by hoarseness and dry cough. Determination of blood antibody levels has shown the prevalence of infection with this organism to be very high, particularly among patients with heart disease.

PCR-based diagnostic studies and clinical studies with antibiotics are now being performed to determine whether these bacteria play a causative role in the development of coronary artery plaques or are merely passive colonisers of them. Should the chlamydial hypothesis be confirmed, future myocardial infarction patients will need to be treated with antibiotics.

Polymerase Chain Reaction (PCR1)