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Single-swab technique simplifies sample collection for infectious keratitis
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Patients with suspected infectious keratitis had a similar culture positivity rate when randomized to either a single-sample device or to the traditional multi-sample method, according to a study.
In the Corneal Ulcer One-Touch Study, 81 eyes of 80 consecutive patients were sampled, 41 eyes with culture plates and 40 eyes with ESwab (Copan Diagnostics), for which the culture positivity rate was 70% and 69%, respectively.
The study also found that ESwab sensitivity was 84%, specificity was 67%, and positive and negative predictive values were 86% and 64%, respectively.
“The sensitivity, specificity, and positive and negative predictive values for ESwab were calculated in comparison to the current gold standard of treatment, the traditional multi-sample method,” principal investigator Kaivon Pakzad-Vaezi, MD, told Ocular Surgery News. However, the study does not state these values for the traditional method, so that is an inherent limitation of the results, he said.
“ESwab is being compared to a technique that does not have perfect sensitivity and specificity, despite being the current gold standard,” Pakzad-Vaezi said.
Even so, the authors found it noteworthy that the traditional method had a higher proportion of culture results with two or more organisms from a single patient than did the ESwab: 42% vs. 23%, respectively.
“All such multi-organism cases included a gram-positive organism known to be contiguous with the ocular surface,” Pakzad-Vaezi said. “Although this was not initially expected, we felt that this may reflect the potential for single-sample vials to have a lower likelihood of contamination, both due to fewer trips to and from the eye and also shorter exposure time of open culture plates.”
Simon P. Holland
ESwab incorporates a spray-on flocked fiber technology, with the tip comprised of many parallel nylon fibers.
“This improves sample collection, with increased capillary action and hydraulic liquid uptake,” co-author Simon P. Holland, MD, said.
The flocked fiber arrangement also improves specimen release, with less entrapment than traditional swab materials. Furthermore, the collection medium maintains bacterial viability for up to 48 hours and up to 6 months for polymerase chain reaction testing.
“Most notably, though, ESwab can be stored for 18 months at room temperature, while broths expire after 1 year at room temperature and agar plates after 2 months’ refrigeration,” Holland said.
Holland said there is a minimal learning curve to using single-sample technology, and patients prefer having fewer samples taken.
Because the bacterial load is relatively low for corneal ulcers, it is important in a single-sample approach to gently but thoroughly roll and scrape the ulcer base and edges with the swab, which has a rigid, bristly nature to facilitate obtaining infected tissue, according to Holland.
The authors, however, do not advocate that clinicians rely solely on the single-swab technology.
“This is a preliminary study. The decision on which culture media to include remains dependent on good clinical judgment and the context of the infection,” Pakzad-Vaezi said. “For example, a contact lens-related ulcer may require specific sampling for Acanthamoeba.”
The study had insufficient fungal cases, and it was not designed to examine viral and biofilm-associated keratitis; hence, the authors do not believe the traditional approach should be replaced in tertiary centers.
“However, given the difficulty of obtaining and maintaining the range of appropriate unexpired culture media in the office, many community and private practice ophthalmologists choose to treat empirically,” Pakzad-Vaezi said. “Still, we feel that ESwab has particular clinical relevance in this context, given its ease of storage, use and transport; comparable results for bacterial keratitis with the traditional method; and the importance of microbial data to guide appropriate treatment, antibiotic resistance detection and public health measures.” – by Bob Kronemyer
Reference:
Pakzad-Vaezi K, et al. Am J Ophthalmol. 2015;doi:10.1016/j.ajo.2014.09.021.For more information:
Simon P. Holland, MD, and Kaivon Pakzad-Vaezi, MD, can be reached at UBC Department of Ophthalmology & Visual Sciences, Eye Care Centre (VGH), 2550 Willow St., Vancouver, BCV5Z 3N9; email: simon_holland@telus.net and kaivon@interchange.ubc.ca.Disclosure: Holland and Pakzad-Vaezi report no relevant financial disclosures.