The role of smears, cultures, and antibiotic sensitivity testing in the management of suspected infectious keratitis

Trends in the Etiology of Infectious Corneal Ulcers at the F. I. Proctor Foundation

OBJECTIVE

We analyzed laboratory results from corneal ulcers seen from 1976 to 1999 at the Francis I. Proctor Foundation, a referral center in San Francisco, to determine the relative frequencies of pathogens and to analyze for trends in frequencies of the most common pathogens. The results were compared with a previous study of corneal ulcers seen from 1948 to 1976 at the same institution.

METHODS

Ulcers presenting to the Proctor Foundation were Gram stained and cultured using standard techniques. Herpetic corneal ulcers were excluded from the study.

RESULTS

Organisms were isolated from 427 ulcers, 38% of all cases. Two hundred seventy-eight (59%) isolates were gram-positive bacteria, 145 (31%) gram-negative bacteria, 16 (3%) Acanthamoeba spp., and 36 (8%) fungi. Staphylococcus aureus was the most common organism, composing 20% of all isolates, followed by viridans group streptococci (12%), Streptococcus pneumoniae (11%), Pseudomonas aeruginosa (6%), Moraxella spp. (5%), and Serratia marcescens (4%). Over the 24-year study period the proportion of positive cultures decreased and the incidence of S. marcescens increased significantly. Comparing the period of 1948-1976 to 1976-1999, the frequency of S. pneumoniae and P. aeruginosa decreased, and that of S. marcescens increased significantly.

CONCLUSION

The common pathogens associated with corneal ulcers have changed over the past 50 years in Northern California, with S. pneumoniae and P. aeruginosa being isolated relatively less often and S. marcescens being isolated with increasing frequency. The decrease in isolation of organisms over the 1976-1999 period may have resulted from increasing empiric antibiotic treatment by referring ophthalmologists.

Clinical and epidemiological advantages of culturing bacterial keratitis

PURPOSE

To examine how the corneal culture result is associated with the antibacterial treatment response rate of ulcerative keratitis in a prospective cohort study and to determine whether culture confirmation affects the relative treatment effect in randomized clinical trials of bacterial keratitis.

METHODS

The influence of a positive bacterial culture on the rates of antibacterial improvement and cure was estimated by proportional hazards regression among 608 patients with ulcerative keratitis treated with topical ciprofloxacin monotherapy. The interaction of culture confirmation on the relative cure rates of 735 patients enrolled in 4 clinical trials comparing fluoroquinolone monotherapy to combined cephalosporin and aminoglycoside therapy was evaluated by metaregression.

RESULTS

In a prospective cohort study, bacterial keratitis that was culture positive and longer than 4 mm had a 37% (95% confidence interval, 20%, 51%) slower improvement rate and a 56% (95% confidence interval, 41%, 67%) slower cure rate during ciprofloxacin therapy. Among randomized clinical trials, the culture result did not modify the relative effect of treatments having similar 1-week cure rates.

CONCLUSIONS

Culture confirmation affects the antibacterial therapeutic response rate of ulcerative keratitis and, while not modifying the comparative effect of equivalent antibacterial treatments, facilitates generalizability of clinical trials of bacterial keratitis.

The efficacy and safety of topical polymyxin B, neomycin and gramicidin for treatment of presumed bacterial corneal ulceration

AIM

To evaluate the clinical efficacy and safety of topical polymyxin B, neomycin, and gramicidin for the treatment of suspected bacterial corneal ulceration at the Leiden University Medical Center.

METHODS

Patients with a diagnosis of a suspected bacterial corneal ulcer between April 1995 and February 2002 were retrospectively identified and reviewed; clinical and microbiological features and response to therapy were analysed. All patients were treated with Polyspectran eye drops.

RESULTS

In total, 91 patients were included in this analysis. Bacteriological cultures of 46 patients (51%) were positive and revealed 51 microorganisms. Staphylococcus aureus (29.4%) and Pseudomonas aeruginosa (23.5%) were the most frequently encountered bacteria. Eighteen patients switched therapy before complete healing of the corneal ulceration, four patients were lost to follow up. Of the 69 patients who completed Polyspectran treatment, re-epithelialisation occurred in 68 patients (99%) and on average took 12.6 (median 8) days. Among 91 patients, there were four perforations and one evisceration. Seven toxic or allergic reactions were reported.

CONCLUSION

This study shows that the combination of polymyxin B, neomycin, and gramicidin is an effective and safe treatment of suspected corneal ulceration.

Culture Plate Temperature and Delayed Incubation Effect on Bacterial Recovery

PURPOSE

To discover if initial culturing conditions (plate temperature and time delay to incubation) adversely influence the recovery of organisms associated with bacterial keratitis.

METHODS

The rate of temperature equilibration of culture plates taken from a refrigerator and placed in an incubator and left on the desk was evaluated with a digital thermometer. A standard inoculum for each of five organisms (S. aureus, S. pneumoniae, P. aeruginosa, E. aerogenes, K. oxytoca) isolated from human bacterial keratitis was spread evenly on blood agar plates at refrigerator (Tcold; 4 degrees C), room (Troom; 24 degrees C), and incubator (Twarm; 37 degrees C) temperatures. The plates were then kept at room temperature for 0, 1, 3, 5, and 8 hours before overnight incubation at 37 degrees C (S. pneumoniae under microaerophilic conditions), and the number of colony-forming units was counted.

RESULTS

Cold plates took at least 15 minutes in an incubator to attain room temperature, and up to an hour when left on the desk. Increased organism recovery was found comparing both Twarm and Troom plates (6.2 to 24.8% and 7.0 to 14.7%, respectively, P<0.001) to Tcold plates for all organisms except S. pneumoniae (P=0.057). Comparing Twarm plates to Troom plates demonstrated an increased recovery (P<0.001) for S. aureus. Delayed incubation resulted in decreased recovery for S. pneumoniae (P<0.001).

CONCLUSIONS

Culture plates should preferably be warmed at least to room temperature before inoculation, as well as promptly incubated to increase bacterial recovery from cases of septic keratitis.

Severe infective keratitis leading to hospital admission in New Zealand

AIM

To identify key risk factors and the management and outcome of severe infective keratitis leading to public hospital admission in New Zealand.

METHODS

Over a 2 year period, all admissions of presumed infective keratitis to Auckland Hospital were identified. The clinical records of all 103 cases were retrospectively reviewed with respect to clinical features, risk factors, management, and outcomes.

RESULTS

The mean time from first symptoms or signs and presentation to hospital was 8.9 (SD 15.5) days. The majority of subjects, 88%, had at least one of the risk factors commonly associated with infective keratitis including previous ocular surgery (30%), contact lens wear (26%), topical corticosteroid use (25%), and ocular trauma (24%). Corneal scraping was performed in 92% and of a total of 105 scrapes, 71% were positive. Bacteria were isolated in all these cases, the majority being Gram positive organisms (72%). The most common isolates identified were coagulase negative Staphylococcus (16%), Propionibacterium acnes (14%), Staphylococcus epidermidis (11%), and Streptococcus pneumoniae (9%). In addition, yeasts were isolated in 5%, fungi in 4%, virus in 2%, and chlamydia in 1%. Importantly, polymicrobial infection accounted for 33% of culture positive cases. Antimicrobial treatment was changed on the basis of culture results in 17 cases (16.5%). Median initial visual and final best corrected visual acuity was 6/36-6/48 (logMAR 0.86) (IQR 0.39-2.00) and 6/12-6/15 (logMAR 0.360) (IQR 0.15-1.70), respectively. Previous ocular surgery and topical corticosteroid use were significantly associated with poorer visual acuity. The mean hospital stay was 5.8 days and the median 4.0 (IQR 2.0-8.0) days. Longer duration of stay was associated with the presence of hypopyon, larger ulcers, previous ocular surgery, and poor visual acuity.

CONCLUSIONS

Infectious keratitis is an important cause of ocular morbidity. A significant proportion of cases have potentially modifiable risk factors. Previous ocular surgery and topical corticosteroid use, in particular, were associated with poorer visual outcomes. Many cases of severe keratitis might be avoided, or their severity reduced, by appropriate education of patients and ophthalmologists.

Simplifying collection of corneal specimens in cases of suspected bacterial keratitis

Identification of the causative organisms in suspected bacterial keratitis traditionally involves collecting multiple corneal scrapes, which are plated directly onto different solid agar culture media. Difficulties have been reported with this practice, so the development of a simpler diagnostic method in suspected bacterial keratitis would be useful. It is unclear whether a single corneal scrape sent to the microbiology laboratory in a liquid transport culture medium (indirect method) is as reliable for the diagnosis of bacterial keratitis as inoculation of multiple scrapes directly onto agar plates (direct method). To investigate this, bacterial recovery was assessed following transfer and transport of different concentrations and types of bacteria from an artificially contaminated surgical blade into brain heart infusion (BHI). Bacterial recovery rates between the proposed (indirect) and standard (direct) method were then compared after the in vitro inoculation of pig corneas and following specimen collection in patients with presumed bacterial ulcerative keratitis. Recovery of bacteria from contaminated surgical blades was found to be the same from both solid and liquid culture media. There was no significant difference in the numbers of positive cultures from solid (direct) and liquid (indirect) culture media, both in the experimental pig cornea inoculation study (P = 0.34) and in experiments with patients with clinical infections (P = 0.4), with an 85.2% agreement between methods (kappa = 0.61, P < 0.0001). In conclusion, therefore, the collection of two corneal scrapes, one used for Gram staining and the other transported in BHI followed by plating and subculturing in an enrichment medium, provides a simple method for the investigation of presumed bacterial keratitis.

Bacterial keratitis: predisposing factors, clinical and microbiological review of 300 cases

AIM

To identify predisposing factors and to define clinical and microbiological characteristics of bacterial keratitis in current practice.

METHODS

A retrospective analysis of the hospital records of patients presenting with bacterial keratitis and treated at the Quinze-Vingts National Center of Ophthalmology, Paris, France, was performed during a 20 month period. A bacterial keratitis was defined as a suppurative corneal infiltrate and overlying epithelial defect associated with presence of bacteria on corneal scraping and/or that was cured with antibiotic therapy. Risk factors, clinical and microbiological data were collected.

RESULTS

300 cases (291 patients) of presumed bacterial keratitis were included. Potential predisposing factors, usually multiple, were identified in 90.6% of cases. Contact lens wear was the main risk factor (50.3%). Trauma or a history of keratopathy was found in 15% and 21% of cases, respectively. An organism was identified in 201 eyes (68%). 83% of the infections involved Gram positive bacteria, 17% involved Gram negative bacteria, and 2% were polymicrobial. Gram negative bacteria were associated with severe anterior chamber inflammation (p=0.004), as well as greater surface of infiltrates (p=0.01). 99% of ulcers resolved with treatment, but only 60% of patients had visual acuity better than the level at admission, and 5% had very poor visual outcome.

CONCLUSIONS

Contact lens wear is the most important risk factor. Most community acquired bacterial ulcers resolve with appropriate treatment.

Efficacy of transport media use versus direct inoculation of blood agar plates in the microbiologic evaluation of experimental Streptococcus pneumoniae keratitis

PURPOSE

To compare the microbiologic yield of cultures obtained by direct inoculation of blood agar plates (BAP) from corneal ulcer swabbings versus indirect inoculation via transport media in a rabbit model of Streptococcus pneumoniae bacterial keratitis.

METHODS

The corneas of 12 rabbits were inoculated with S. pneumoniae. Keratitis was confirmed 18 hours later. Sampling was performed at four 2.5-hour intervals. At each interval, corneal swabs were directly applied to BAP and placed into transport medium: thioglycollate and Amies medium without charcoal. Swabbings were then subcultured onto BAP at two time points: 2 and 24 hours after collection in transport medium. Plates were evaluated 48 hours later. Organism recovery rates were measured in terms of the number of positive culture plates observed and the bacterial colony counts on each plate.

RESULTS

The rate of positive cultures overall was 69%. The recovery rates were similar for direct inoculation, inoculation via Amies held for 2 hours, and inoculation via Amies held for 24 hours. Direct inoculation yielded fewer colonies than indirect inoculation via Amies held for 24 hours (p = 0.008). Direct inoculation yielded a higher rate of positive cultures than did thioglycollate held for 2 hours (p = 0.004) or 24 hours (p < 0.001). The rate of nonpneumococcal contaminants ranged from 6% of BAP subcultured from thioglycollate held for 24 hours to 28% of directly inoculated BAP.

CONCLUSIONS

Amies medium without charcoal may be used as a transport medium for up to 24 hours in the recovery of S. pneumoniae from corneal ulcers in this rabbit model. Thioglycollate appears to be less effective as a transport medium. Results of this study may justify studies of other transport media and/or other corneal pathogens. Altogether, such studies may provide justification for human clinical trials.

Does identification of the causal organism of corneal ulcers influence the outcome?

PURPOSE

To investigate whether identification of the causal organism in corneal ulcers influences their outcome.

METHODS

We retrospectively studied 114 patients, 72 males and 42 females aged 6-89 years, admitted to this eye clinic during the years 1994-2000 on account of an infectious corneal ulcer. Their examination included a detailed history, visual acuity measurement, and biomicroscopy in everyday follow-up. The ulcers were classified according to their severity and outcome. We assessed the cases where cultures had been done, reviewed the results, and searched for a possible correlation between the outcome and the fact of culturing the ulcer and identifying the causal organism.

RESULTS

Of the 114 corneal ulcers studied, 23 were mild, 49 moderate, and 42 severe. Fifty (44%) had not been cultured, but 64 ulcers (56%) had been cultured, with a positive result in 37 cases (58%), Staphylococcus and Pseudomonas species being the most common organisms found. In moderate and severe ulcers, there was a tendency to a higher proportion of successful outcome for cultured ulcers, but with no significant correlation.

CONCLUSIONS

Despite a tendency towards favorable results in culture-positive corneal ulcers, the influence of the detection of the organism on their outcome has not been proved. The role of the initial broad-spectrum antibiotic therapy remains important.

Evaluation of corneal scraping smear examination methods in the diagnosis of bacterial and fungal keratitis: a survey of eight years of laboratory experience

PURPOSE

To determine the sensitivity, specificity, and predictive values of Gram and potassium hydroxide with calcofluor white (KOH+CFW) stains in the diagnosis of early and advanced microbial keratitis, a retrospective analysis of comparative data from a prospectively collected database was done.

METHODS

Patients with nonviral microbial keratitis seen at L.V. Prasad Eye Institute between February 1991 and December 1998 were included in the study. The type of bacteria seen on Gram stain was determined from 251 corneal scrapings from patients with early keratitis and 841 corneal scrapings from patients with advanced keratitis. The presence of fungi in corneal scrapings was determined by KOH+CFW stain of 114 and 363 scrapings from patients with early and advanced keratitis, respectively. The smear findings were compared with culture results to analyze specificity, sensitivity, and predictive values of the staining techniques.

RESULTS

The sensitivity of Gram stain in the detection of bacteria was 36.0% in early and 40.9% in advanced keratitis cases; however, the specificity was higher in both groups (84.9% and 87.1%, respectively). Comparatively, the sensitivity and specificity of fungal detection were higher using KOH+CFW in early (61.1% and 99.0%, respectively) as well as advanced keratitis (87.7% and 83.7%, respectively). Predictive values were high for KOH+CFW in fungus detection, while they were poor for Gram stain in bacteria detection. In advanced keratitis cases, the false positives were higher in fungal detection (16.3%) than in bacterial detection (10.3%), while the false negatives were significantly higher in bacterial detection compared with fungal detection (59.1% versus 12.3%, p< 0.0001). In early keratitis, on the other hand, both false positives and false negatives for bacterial detection were significantly higher than fungal detection.

CONCLUSIONS

Decisions can reliably be based on KOH+CFW stain of corneal scrapings for initiation of antifungal therapy in mycotic keratitis. The results of Gram stain, on the other hand, have limited value in therapeutic decisions for bacterial keratitis. Therefore, the search for a better modality for early and efficient diagnosis of bacterial keratitis needs to continue.

Management of blebitis by members of the American Glaucoma Society: a survey

PURPOSE

To investigate the practice patterns among glaucoma subspecialists in the American Glaucoma Society regarding the management of blebitis.

METHODS

An anonymous survey incorporating 14 questions regarding the management of blebitis was mailed to all current active American Glaucoma Society members, including provisional members, in October 1999.

RESULTS

A total of 319 physicians received the survey, and 204 members (64%) returned surveys. Sixty-nine percent of respondents do not ask their patients with functioning blebs to use topical antibiotics at home for early symptoms of blebitis. Thirty-four percent never or almost never obtain conjunctival cultures at the onset of isolated blebitis, whereas 44% always or usually do. Fifty-one percent prescribe a topical fluoroquinolone alone as the initial empirical treatment of isolated blebitis. Twenty-three percent use a fluoroquinolone in combination with one or two other antibiotics. Twenty-one percent choose a combination of fortified topical agents, usually including a fortified aminoglycoside, vancomycin, or cephalosporin. Thirty-one percent use fortified agents in some combination with or without a fluoroquinolone. Five percent prescribe some other single agent alone. Only 6% routinely use an oral antibiotic in cases of blebitis. Sixty-two percent use topical corticosteroids in conjunction with antibiotic treatment. Of these, 68% start them after initial antibiotic treatment is established or once improvement of blebitis is noted. Fifty-six percent indicated that a moderate or severe anterior chamber reaction, including fibrin, would prompt treatment as a possible endophthalmitis. In a persistently Seidel-positive bleb, 77% generally attempt surgical bleb revision.

CONCLUSIONS

Methods of the management of blebitis differ among members of the American Glaucoma Society. Treatment recommendations generated from randomized clinical trials are needed.

Aspergillus fumigatus keratitis with wreath pattern infiltrates

PURPOSE

To report a case of Aspergillus fumigatus keratitis with clinical features simulating Nocardia keratitis and to highlight the utility of microbiologic investigation in the successful management of infectious keratitis.

METHOD

Case report.

RESULTS

A 62-year-old man presented with complaints of pain, redness, and watering of 10 days' duration in his right eye. Direct microscopic observation of smears of corneal scrapings revealed a fungal etiology. The patient was treated with 5% natamycin eye drops and 1% atropine sulphate eye drops and was advised to visit the hospital for observation. During his visit to the hospital on day 10 after medication, the eye demonstrated a wreath pattern corneal infiltrate that simulated Nocardia keratitis. The fungus grown from culture of corneal scraping was identified as A. fumigatus.

CONCLUSION

This report highlights the significance of subjecting corneal scrapings from suspected cases of infectious keratitis to microbiologic evaluation and emphasizes the fact that a complete microbiologic work-up helps in establishing a definitive etiologic diagnosis and initiating specific antimicrobial therapy.

The evolution of antibiotic therapy for bacterial conjunctivitis and keratitis: 1970-2000

The editors of this Festschrift asked us to review the use of antibiotics for the treatment of bacterial conjunctivitis and keratitis over the past 25 years, a period coinciding with the life of the Castroviejo Corneal Society. We believe it is more appropriate to begin our review in the late 1960s. about the time that experimental and clinical studies and algorithms for the clinical care derived from these studies helped shape a more rigorous approach to therapy. Those years saw the introduction of antibiotics that were adapted for ophthalmic use, many of which are still being used today. We will give more weight to our review of keratitis than conjunctivitis.

Study of the first contact management profile of cases of infectious keratitis: a hospital-based study

PURPOSE

To study the management pattern and examine the role of cultures and antibiotic sensitivity testing in infectious keratitis.

METHODS

A retrospective analysis of the demographic, clinical, and microbiological data was performed in 100 consecutive patients with infectious keratitis. The main parameters evaluated were nature of first contact with the health care services, investigations undertaken, treatment initiated, and the time interval between presentation to the first medical contact and to our center. Finally, the reports of culture and antibiotic sensitivity testing undertaken at our center were evaluated.

RESULTS

In 70% of cases, ophthalmologists in independent practice were the first medical contact. Direct microscopy of the corneal scraping was undertaken in only 6% of cases, whereas culture and sensitivity studies had not been performed in any of the patients. Forty-six percent of the patients were prescribed 0.3% ciprofloxacin eyedrops in an inadequate dosage. Broad-spectrum fortified antibiotics eye drops had not been prescribed in any of the cases. At our center, positive cultures were obtained in 73.86% of cases and the most common organism isolated was coagulase-negative Staphylococcus (33.84%), followed by Pseudomonas aeruginosa (15.38%). A large number of the isolates demonstrated resistance to the recommended antibiotic therapy.

CONCLUSIONS

Failure to implement standard management protocol for infectious keratitis at first contact is a major factor contributing to ocular morbidity in India.

Comparison of topical 0.3% ofloxacin with fortified tobramycin plus cefazolin in the treatment of bacterial keratitis

PURPOSE

Ofloxacin is a broad spectrum fluoroquinolone antibiotic with good ocular penetration. We compared ofloxacin 3% solution with a combination of fortified tobramycin sulphate and cefazolin sodium solutions in the treatment of culture-proven bacterial keratitis.

METHODS

Thirty eyes with culture-proven bacterial corneal ulcers were enrolled in a prospective randomised, controlled, double-masked study for comparison. The ofloxacin drop and saline were decanted into two identical-looking bottles to the tobramycin and cefazolin. The cases were randomly allocated into treatment with 0.3% ofloxacin solution or a combination of fortified antibiotics (1.5% tobramycin and 10% cefazolin solutions; control group) along with supportive cycloplegic, vitamins and anti-glaucoma therapy. Student's t-test was used to compare the results.

RESULTS

Staphylococcus aureus and coagulase-negative staphylococci were the two most common organisms isolated. Resolution of the ulcer was achieved in 93% and 87% of cases in the ofloxacin and control groups respectively. The mean time required for symptomatic relief was 7.8 +/- 1.54 days and for epithelial healing 15.0 +/- 3.86 days in ofloxacin group, compared with 8.33 +/- 1.54 days for symptomatic relief and 15.46 +/- 3.86 days for epithelial healing in the control group. Post-resolution best corrected visual acuity of 20/200 or better was achieved in all but one eye in both groups.

CONCLUSIONS

Ofloxacin and combined fortified tobramycin and cefazolin topical drops were comparable for treating cases of bacterial corneal ulcer. However, considering its easy availability and cost-effectiveness, monotherapy with ofloxacin is preferred over the combined fortified tobramycin and cefazolin therapy.

Risk factors for treatment outcome of suspected microbial keratitis. Ofloxacin Study Group

BACKGROUND

Primary treatment for suspected microbial keratitis is generally successful. Although risks such as contact lens use are well recognised as causative factors for microbial keratitis, little is known about the risk factors that influence treatment outcome. The present study evaluates the risk factors assessed at diagnosis as prognostic indicators of primary treatment failure.

METHODS

Patients were prospectively enrolled in the ofloxacin treatment trial and data concerning symptoms, treatments, past and concurrent eye disease were collected along with the measurement of corneal ulcer size at the slit lamp. All patients were scraped for microbiological investigation, and treated with either ofloxacin (0. 3%) or standard therapy of fortified cefuroxime and gentamicin drops. Treatment success was complete healing of the ulcer with zero dimensions of the epithelial defect within 2 weeks of start of treatment. The important prognostic indicators were selected by comparison among those who failed treatment, had delayed healing, or were culture positive with other patients using univariate and stratified analysis. These were then used in a Poisson model for multiple regression analysis to estimate the relative risk of the main prognostic variables.

RESULTS

Of the 118 patients enrolled in the study, 14 were identified as primary treatment failures, 17 had slow healing, and 15 indolent ulcers. There were 49 culture positive patients. The multivariate analysis identified that large culture positive ulcers in patients 60 years or older had 5.5 times the risk of primary treatment failure (p<0.001). Significant predictors of slow healing were previous ocular disease and a positive culture; significant predictors of indolent ulceration were previous ocular disease and steroid use at diagnosis; the main predictor of a culture positive result was ulcer size.

CONCLUSIONS

Elderly patients with large ulcers were more likely to be culture positive, fail primary therapy, and require surgical intervention. A positive microbial culture provided prognostic information regardless of the organism isolated. However, this information was of less value for those with small ulcers and for younger patients.

Corneal biopsy with tissue micro-homogenisation for isolation of organisms in bacterial keratitis

PURPOSE

To evaluate a novel two-stage technique to increase yield of bacteria isolated from infected corneal ulcers.

METHODS

A new blade was designed to remove friable material from infected corneal ulcers. The new blade was used in combination with standard tissue micro-homogenisation equipment in a two-stage technique intended to distribute biopsy samples evenly between relevant agar plates. Patients with presumed-bacterial corneal ulcers underwent sequential corneal sampling using the new two-stage technique and a scalpel blade, used without micro-homogenisation (the order of sampling was varied between two groups). Bacterial isolation rates were compared using the chi-squared test.

RESULTS

Twenty-four patients with presumed-bacterial corneal ulcers were studied. The overall positive bacterial isolation rate was 88%, with identical bacterial isolation rates for the new two-stage technique and the scalpel blade (71%). The new technique isolated bacteria from three ulcers that had initially been 'sterile' when sampled with a scalpel blade. Polymicrobial infections were identified in two ulcers with the new blade where only a single organism had been identified using the scalpel blade (not significantly different).

CONCLUSIONS

The new two-stage technique shows promise for improving bacterial isolation rates from presumed-bacterial corneal ulcers.

Culture-negative ulcerative keratitis after laser in situ keratomileusis

A 40-year old man, highly myopic in both eyes, had laser in situ keratomileusis (LASIK) in the left eye in November 1996. Corneal melting and ulceration and fine striae-like interface infiltrates were noticed 1 day postoperatively. There was no response to intensive topical antibiotics in the form of hourly ofloxacin 3% (Tarivid), and satellite lesions developed on day 4. Corneal scrapings for gram stain and culture were done twice. No bacterial or fungal organisms were identified. Intensive topical fortified vancomycin (50 mg/mL) was added, and the lesions resolved gradually over the ensuing 2 weeks. Eighteen months after LASIK, refraction was -1.50 - 0.75 x 105 in the left eye, and uncorrected visual acuity was 20/70, correctable to 20/25 with spectacles.

Bacteriological profile of ophthalmic infections in an Israeli hospital

AIM

To find the optimal antibiotic treatment for ophthalmic infections in an Israeli hospital.

METHODS

In a retrospective study from our laboratory, which serves as both a primary and secondary referral center, we analyzed the bacteriological profile and the antibiotic sensitivity of ophthalmic infections using the computerized laboratory reports of 331 consecutive ophthlamic bacteriological cultures from patients with various ophthalmic infections.

RESULTS

Microbiological growth was obtained in 113 samples (34.1%). The most commonly isolated organism was coagulase-negative staphylococcus (19.5%), followed by coagulase-positive staphylococcus (16.8%), Enterobacteriaceae (14.2%), Pseudomonas aeruginosa (13.3%), and streptococcal species (8.9%). Pseudomonas species were the most common isolates from the lacrimal pathways (20.0%). Streptococci were the most common isolates cultured from the conjunctiva (27.3%). Coagulase-positive staphylococcus was the most common isolate from corneal ulcers (33.3%), and coagulase-negative staphylococcus from the vitreous (30.8%). The overall antibiotic sensitivity of common ophthalmic pathogens was similar to that reported from other parts of the world.

CONCLUSIONS

Although essentially similar to previous series, this report from the Middle East differs as follows. Firstly, Pseudomonas species were the most common isolates from the lacrimal pathways. Secondly, the overall rate of streptococcal isolates was lower than in previous reports. Thirdly, streptococcal species were rarely isolated from corneal samples. Although other studies from the region have described the causative organisms of ocular infections in specific ocular sites, this is the first study from the Middle East to summarize the full bacteriological profile of ocular infections in one medical center.

Topical pefloxacin in bacterial keratitis

PROBLEM

To evaluate the clinical efficacy and safety of topical pefloxacin 0.3% drops as the sole antibiotic used to treat culture positive bacterial corneal ulcers.

METHODS

Forty two consecutive Gram's smear-positive cases of bacterial corneal ulcers were enrolled for this prospective open labelled clinical trial. All patients underwent a complete clinical and microbiological work up and were put on topical 0.3% pefloxacin drops with supportive cycloplegic, vitamins and antiglaucoma therapy. Of 42 cases, 4 cases of mycotic keratitis and 6 culture negative cases were excluded from the study.

RESULTS

Positive microbiologic cultures were obtained in 84.2% (32 of 38) cases. Staphylococcus aureus (14/32; 43.7%) and coagulase negative Staphylococci (12/32; 37.5%) were the two most common organisms isolated. Resolution of the corneal ulcer was achieved in 31 out of 32 cases (96.9%) with a mean duration of 9.3+/-5.3 days (range 3-21 days). Best corrected visual acuity of 20/200 or better was achieved in 65.6% of cases at 4 weeks post resolution. Corneal deposits were observed in one case which disappeared 8 days following discontinuation of therapy.

CONCLUSIONS

Topical pefloxacin is effective as a single antibiotic agent for the treatment of bacterial keratitis.

The utility of culturing corneal ulcers in a tertiary referral center versus a general ophthalmology clinic

OBJECTIVE

The purpose of the study is to compare the utility of culturing corneal ulcers in a tertiary referral clinic and a general ophthalmology clinic.

DESIGN

A retrospective review of medical and microbiologic records was performed.

PARTICIPANTS

One hundred fifty-seven patients with corneal ulcers were included in the study. Eighty-two ulcers were treated in the referral clinic and 75 ulcers were treated in the general ophthalmology clinic.

MAIN OUTCOME MEASURES

The authors determined the percentage of corneal ulcers in each clinical setting that failed to respond to empiric therapy and required a culture-directed change in treatment.

RESULTS

One hundred fifty-seven ulcers were included. Eight (10%) of the 82 patients treated in the Cornea Clinic had treatment altered based on culture and sensitivity results. All 75 patients in the general clinic responded to empiric antibiotics, such that culture data never were required for modification of therapy (0%, P = 0.007). In contrast to patients treated in the Cornea Clinic, patients treated in the general clinic had smaller, more peripheral ulcers, shorter duration of symptoms, and fewer risk factors for corneal ulceration other than contact lens wear.

CONCLUSIONS

Cornea specialists, who are referred the most severe cases, should consider culturing most corneal ulcers. However, it appears reasonable for general ophthalmologists to use culturing more judiciously. Patients with significant corneal ulcers should be cultured regardless of the clinic to which they present. However, small, peripheral ulcers respond extremely well to current, broad-spectrum antibiotics. Close follow-up is mandatory to discover the rare patient who will not respond to empiric therapy.