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Escherichia coli O157 is one of the most common serotypes of shiga-like toxin producing E coli, and has been associated with serious disease and several high profile outbreaks.1
The Quix™ Rapid E coli O157 Strip Test (Universal HealthWatch Inc, Columbia, North Carolina, USA) is an immunochromatographic test that detects the O157 antigen using a colloidal gold labelled antibody. We chose to evaluate the Quix™ Strip Test for the detection of E coli O157 in faecal specimens of patients with bloody diarrhoea or clinical symptoms typically associated with E coli O157 infection, such as haemolytic uraemic syndrome.1
Two hundred and fifty eight consecutive patient specimens referred to our routine diagnostic laboratory with indications described above were entered into our study. Performance of the Quix™ Rapid E coli O157 Strip Test was compared with growth on sorbitol MacConkey agar, a method used for routine detection of E coli O157 in our laboratory.2 The test was performed according to the manufacturer’s instructions. Briefly, a sample of faeces approximately 5 mm in diameter was suspended in five drops of buffer solution. A strip was placed in the tube and the sample allowed to migrate along the strip for five minutes. The results were then read directly from the strip.
Of the 258 specimens included in our study, eight yielded E coli O157 on sorbitol MacConkey agar and all eight specimens were identified using the Quix™ Rapid E coli O157 Strip Test.
Of the 250 E coli O157 negative specimens, all were negative using the Quix™ Rapid E coli Strip Test.
We also tested a sample previously culture positive for E coli O157 that had been stored at 4°C for six months. This produced a positive result with the Quix strip, despite no growth on re-culture. This demonstrates that the strip test can function in the absence of viable bacteria, and therefore may be used for the retrospective study of specimens.
Limitations of the test include the high cost and inability to detect serotypes of shiga-like toxigenic E coli other than O157. Few studies have assessed the frequency at which non-O157 serotypes cause disease, although a two year study in Canada reported that non-O157 shiga-like toxigenic E coli were isolated from 0.7% of patient specimens.3 Further evaluation of the incidence of non-O157 shiga-like toxigenic E coli would be required to determine the value of the Quix Strip Test.
The results of our limited study suggest that the strip test is highly sensitive and specific and larger scale studies may be warranted. The rapid turn around time is advantageous, providing clinicians with a prompt diagnosis, and the test may prove suitable for near patient testing. Overall, the Quix™ Rapid E coli O157 Strip Test was quick, accurate, and simple to use.