13 March 2012
The Health Protection Agency (HPA) is investigating inaccurate results given by a commercially available syphilis test kit that was used in conjunction with other tests to diagnose syphilis between November 2010 and September 2011.
As a result of the problem with these test kits, which are no longer on the market, a small number of people were diagnosed with syphilis when they did not have the infection, and some people were diagnosed as having early stage syphilis when they actually had late stage disease. Those people who received a negative test result have not been affected by this incident.
Following an extensive ‘lookback’ exercise, around 75 people have been identified as possibly being affected by this problem. Further rechecking of samples from these patients is underway and anyone given an incorrect diagnosis will be informed of their correct diagnosis and, where necessary, will receive further treatment.
Those people who may have been given an incorrect diagnosis due to anomalies in the function of the test kit represent only a very small proportion of the people tested for syphilis in the UK each year - approximately 1.5 million tests are carried out annually.
The HPA has been leading the investigation into the impact of the results from affected batches of the particular kit, which was the subject of a Field Safety Notice from the manufacturer in August 2011 and a Medical Device Alert by the Medicine and Healthcare Products Regulatory Agency (MHRA) in November 2011, to stop other laboratories using the affected kits.
It was the national reference laboratory for sexually transmitted infections at HPA Colindale that first spotted the problem and alerted the manufacturers and the MHRA. Two HPA laboratories and six non-HPA laboratories across the UK (including three in Scotland and one in Wales) used the affected kits during the period in question.
The test kit in question is designed to detect an antibody called immunoglobulin M (IgM) and is one of a series of four laboratory tests used to diagnose syphilis. The affected batches of test kits gave higher levels of ‘positive’ results than would be expected, meaning they incorrectly suggested the presence of the syphilis IgM antibody when it was not actually present.
As the results of all four tests are used along with clinical symptoms in making the diagnosis of syphilis, only in a very small number of cases have people been given the incorrect diagnosis or incomplete treatment - in the great majority of cases the right diagnosis has been given.
Professor Cathy Ison, director of the Sexually Transmitted Bacterial Reference Laboratory at HPA, said: “When we noticed an increase in false positives from this commercial test kit we alerted the manufacturer. They subsequently issued a product safety notice for three batches of their kits and the MHRA issued an alert.
“All the laboratories, including those in the HPA, that were using this test have taken this incident extremely seriously and are taking every step to ensure those affected are informed of their correct diagnosis. With the help of laboratories and sexual health doctors across the country, we have been investigating which patients received an incorrect diagnosis and we are now in the process of working with doctors to ensure that anyone affected is informed of their correct diagnosis and given further treatment if necessary.
“Anyone incorrectly diagnosed with syphilis when they did not have the infection will have been prescribed a limited course of antibiotic treatment. This will not have had any lasting impact on their health. Anyone diagnosed with early stage syphilis when they actually had late stage disease may require additional antibiotics to completely clear the infection and prevent any complications. However, as patients with late stage syphilis are not usually infectious, it is very unlikely that they could have passed the infection on to anyone else.
“We would like to reassure the public that anyone who received an incorrect diagnosis will be contacted by their clinic within the coming weeks.”
Around 5,000 cases of syphilis are diagnosed in the UK each year. Initial presentation is usually a single painless but highly infectious ulcer which appears at the site of infection, but many syphilis diagnoses are made in individuals with no symptoms who are screened for the infection. Syphilis is also an easily treatable infection and can be prevented by sexually active people consistently wearing condoms with all new and casual sexual partners and by reducing the number of sexual partners they have.
Last reviewed: 13 March 2012