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Calcium alginate swab versus Bard Parker blade in the diagnosis of microbial keratitis
P Jacob1, U Gopinathan, S Sharma
1Sight Savers' Corneal Training Centre, L. V. Prasad Eye Institute, Hyderabad, India.
Abstract:
A prospective comparative evaluation of Bard Parker blade no. 15 and calcium alginate swab in the collection of corneal material was conducted. The study group included 30 consecutive cases of bacterial (n = 17), fungal (n = 11), and mixed (n = 2) cases of microbial keratitis. The samples collected by blade and swab were processed in an identical manner for viable colony counts. The yields from blade and swab were compared using the proportion test, taking into consideration the mean counts of each organism. The swab yielded significantly greater growth than blade (p = 0.003) in mycotic ulcers. However, the two patients (2/11) who showed no growth by blade but were positive by swab had smears positive and were diagnosed as mycotic ulcers. The difference between the two methods was not significant for bacterial and mixed ulcers. Replacement of blade with calcium alginate swab did not appear to be advantageous for the investigation of infectious keratitis.
Insights
For fungal keratitis, calcium alginate swabs showed significantly better microbial growth than Bard Parker blades. However, for bacterial and mixed ulcers, blade collection was equally effective, suggesting swabs are not universally advantageous for infectious keratitis diagnosis.
Area of Science:
- Ophthalmology
- Microbiology
- Infectious Diseases
Background:
- Microbial keratitis is a serious eye infection requiring prompt diagnosis.
- Accurate sample collection is crucial for identifying causative pathogens.
- Bard Parker blades and calcium alginate swabs are common tools for corneal scraping.
Purpose of the Study:
- To compare the efficacy of Bard Parker blade no. 15 and calcium alginate swabs in collecting corneal material for microbial analysis.
- To determine if calcium alginate swabs offer an advantage over blades in diagnosing infectious keratitis.
Main Methods:
- A prospective comparative study involving 30 patients with microbial keratitis.
- Corneal samples were collected using both a Bard Parker blade and a calcium alginate swab.
- Samples were processed for viable colony counts, and yields were compared using the proportion test.
Main Results:
- Calcium alginate swabs yielded significantly greater fungal growth in mycotic ulcers compared to blades (p = 0.003).
- Two cases diagnosed as mycotic ulcers showed positive growth with swabs but not with blades.
- No significant difference in yield was observed between blades and swabs for bacterial or mixed ulcers.
Conclusions:
- Calcium alginate swabs may be advantageous for collecting samples in suspected fungal keratitis.
- The routine replacement of blades with swabs is not demonstrably beneficial for the overall investigation of infectious keratitis.
- Blade collection remains a viable method for bacterial and mixed keratitis sample collection.