The symptoms of and treatment for the new strain, known as new variant Chlamydia trachomatis, do not differ from those for normal chlamydia.

However, it is missing the section of DNA that a number of laboratories use to identify the presence of chlamydia. Around a quarter of samples are processed by laboratories using these tests.

Samples processed by these laboratories would incorrectly give the all clear to a patient infected with the new strain. The laboratories have been advised to look out for unexplained falls in positive results and to consider using different tests.

Health Protection Scotland believes that the incidence of the new strain is likely to be very low, but said it is monitoring the situation carefully. The Health Protection Agency is planning to notify laboratories in England and Wales of the presence of the new strain in the UK.

North London GP Dr Richard Ma, a member of the National Chlamydia Screening Programme committee, said that, although the new strain would not be picked up by some tests, a far larger number of other cases of chlamydia were not being picked up because not enough screening was being done.

'Whether or not there is a new strain, we are still not doing enough screening,' he said. 'GPs and others involved in screening programmes must continue to promote the need to increase participation in such schemes.'

tom.moberly@haymarket.com

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