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To compare the clinical course of Nocardia spp keratitis with keratitis due to other bacterial organisms, and to assess the effect of corticosteroids as adjunctive therapy using data collected from the Steroids for Corneal Ulcers Trial (SCUT).
Sub-group analysis of a randomized controlled trial
Multicenter randomized controlled trial
500 patients with bacterial keratitis, randomized 1:1 to topical corticosteroid or placebo who had received at least 48 hours of topical moxifloxacin
Topical prednisolone phosphate 1% or placebo; clinical course of Nocardia keratitis
Best spectacle-corrected visual acuity and infiltrate/scar size at 3 months from enrollment
Of 500 patients enrolled in the trial, 55 (11%) had a Nocardia corneal ulcer. Patients with Nocardia ulcers had better presentation visual acuity compared to non-Nocardia ulcers (median Snellen 20/45 compared to 20/145, P<0.001), and comparable 3-month visual acuity (median 20/25 versus 20/40, P=0.25). Nocardia ulcers had approximately 2 lines less improvement in visual acuity compared to non-Nocardia ulcers (0.21 logMAR, 95% CI 0.09 to 0.33 logMAR, P=0.001). This difference may reflect the better starting visual acuity in patients with Nocardia ulcers. In Nocardia ulcers, corticosteroids were associated with an average 0.4 mm increase in 3-month infiltrate/scar size (95% CI 0.03 to 0.77mm, P=0.03).
Nocardia ulcers responded well to treatment. They showed less overall improvement in visual acuity than non-Nocardia ulcers, but had better presentation acuity. Corticosteroids may be associated with worse outcomes.
Nocardia spp is a common cause of infectious keratitis in South Asia, where it has been found to be ubiquitous in the soil.1–3 Several large case series have shown that patients with Nocardia keratitis typically have good visual outcomes with appropriate diagnosis and therapy.4,5 However, there is little evidence regarding outcomes of Nocardia keratitis compared to keratitis due to other bacterial organisms, and there is little information on the utility of topical corticosteroids as adjunctive therapy in these cases. Corticosteroids may reduce immune-mediated tissue damage in bacterial corneal ulcers and improve clinical outcomes, however case reports have suggested that topical corticosteroids may cause recurrent infection in Nocardia keratitis.6,7 Additionally, the majority of prior reports have focused primarily on the use of amikacin in the treatment of Nocardia keratitis, but there are few reports on the clinical response to fluoroquinolones.8 The Steroids for Corneal Ulcers Trial (SCUT) was a randomized controlled trial assessing clinical outcomes in patients with bacterial corneal ulcers who received adjunctive topical corticosteroids versus placebo.9 Here, we report the clinical outcomes of Nocardia keratitis cases enrolled in the trial, the susceptibility and response of these cases to fluoroquinolones, and the effect of adjunctive topical corticosteroid therapy on clinical outcomes.
SCUT was an NIH/NEI-funded, multicenter, randomized, placebo-controlled, double masked clinical trial comparing clinical outcomes in patients receiving topical corticosteroid or topical placebo as adjunctive therapy in the treatment of bacterial corneal ulcers. Detailed methods for the trial have been described previously.9 In brief, 500 patients with culture-proven bacterial corneal ulcers were randomized to receive topical prednisolone phosphate (Bausch & Lomb Pharmaceuticals, Inc., Tama, FL) or topical placebo (0.9% NaCl and preservative, prepared by Leiter's Pharmacy, San Jose, CA) after they had received at least 48 hours of topical 0.5% moxifloxacin (Vigamox, Alcon, Fort Worth, TX). The corticosteroid and placebo regimens consisted of 1 drop applied topically 4 times per day for one week, and then twice a day for one week, and then once a day for one week. The moxifloxacin regimen for both arms consisted of 1 drop applied topically every hour while awake for the first 48 hours, then 1 drop applied every two hours until re-epithelialization, and then 4 times a day until 3 weeks from enrollment. Treating physicians were allowed to change or discontinue adjunctive medications and were allowed to discontinue the study medication if they felt it was medically necessary. Exclusion criteria included: evidence of fungus on KOH preparation, Giemsa stain, or culture; evidence of acanthamoeba by stain; evidence of herpetic keratitis by history or examination; use of a topical corticosteroid or systemic prednisolone during the course of the present ulcer; and impending perforation. Enrollment centers included the Aravind Eye Care System (Madurai, Coimbatore, Tirunelveli), Dartmouth-Hitchcock Medical Center, and the Francis I. Proctor Foundation at the University of California, San Francisco.
The primary outcome for the trial was best spectacle-corrected visual acuity (BSCVA) at 3 months from enrollment. Secondary outcomes included infiltrate/scar size at 3 months from enrollment, time to re-epithelialization, and proportion of adverse events including corneal perforation in each arm. Patients were evaluated every 3 days +/− 1 day until re-epithelialization. Infiltrate/scar size and epithelial defect size were measured by slit lamp examination as the longest diameter by the longest perpendicular to that diameter. BSCVA was measured at enrollment and 3 months using an ETDRS “Tumbling E” chart. All measurements were performed by masked examiners certified for the study.
Corneal scraping was performed at presentation. Two scrapings were smeared for Gram stain and KOH wet mount. Three scrapings were inoculated onto sheeps' blood agar, chocolate agar, and potato dextrose agar or Sabouraud's agar. The criterion for a positive bacterial culture was growth of the organism on one solid medium at the site of inoculation, with the exception of diptheroids and coagulase-negative staphylococcus, where more stringent criteria were required.10,11 Antibiotic susceptibility testing for moxifloxacin was performed using the Etest method (AB BIODISK, Solna, Sweden).10,12 Kirby-Bauer disk diffusion (Hi-media, India) was used to test antibiotic susceptibility to amikacin, ciprofloxacin, ofloxacin, gatifloxacin and moxifloxacin, according to CLSI standards.13 Patients with mixed infections were excluded from this ancillary study.
The Nocardia strains were speciated and subtyped by PCR and bi-directional sequencing using methods previously described.14 The sequences obtained were then used to perform nucleotide-nucleotide searches utilizing the BLASTn database at the NCBI website (http://www.ncbi.nlm.nih.gov/BLAST/). BLAST outputs were sorted based on maximum identity, and identifications were made when BLAST searches yielded at least 85% and for closely related species >90% of query coverage.
Demographic and clinical characteristics across Nocardia species were analyzed with a Fisher's exact test for categorical variables or analysis of variance (ANOVA) for continuous variables. Comparisons of three-month BSCVA and infiltrate/scar size in Nocardia spp keratitis versus all other causative organisms were analyzed using multivariate linear regression with a dichotomous term for Nocardia spp versus other causative organisms, controlling for corticosteroid treatment and baseline characteristics (BSCVA or infiltrate scar/size, respectively). The effect of corticosteroid in Nocardia spp on BSCVA and infiltrate/scar size at 3 months was analyzed using a multivariate linear regression controlling for whether the patient had amikacin added to their treatment regimen and baseline BSCVA and infiltrate/scar size, respectively. A sensitivity analysis was performed on the entire dataset, using an interaction term for Nocardia spp by treatment arm (corticosteroid or placebo). A Cox proportional hazards model controlling for baseline epithelial defect size and addition of amikacin to the treatment regimen was used to assess time to re-epithelialization. The geometric mean of the two measurements obtained for infiltrate/scar and epithelial defect size was used in the analyses. Proportion of cases perforating was assessed using a Fisher's exact test. All analyses were performed in Stata 10.0 (StataCorp, College Station, TX).
Of the 500 corneal ulcers enrolled in the trial, 56 (11%) were identified as being due to Nocardia spp. All Nocardia cases were isolated in India. One patient had a mixed infection with Nocardia and was excluded. Nocardia spp was the third most commonly-isolated organism in the trial overall. Of the 55 enrolled Nocardia cases, 32 (58%) reported a history of trauma in the affected eye. Of these, 11 (34%) were due to vegetative matter injury. Nearly half (N=26, 47%) of the patients were agricultural workers. Median age at presentation was 48 years (interquartile range (IQR) 40 to 60 years). Thirty (55%) of the patients were male. The median duration of symptoms prior to presentation was 10 days (IQR 4 to 15 days).
Strain typing results were available for 52 of the 55 samples (95%). The most common species were N. cyriacigeorgica (N=18, 35%), N. pneumoniae (N=11, 21%), and N. asteroides (N=10, 19%) (Table 1). Ninety-eight percent of Nocardia spp were susceptible to amikacin. The fluoroquinolones tested by Etest and disk diffusion had variable activity against the Nocardia species, ranging from 45% of N. pneumoniae isolates susceptible to moxifloxacin and ciprofloxacin to 100% susceptibility against N. farcinica. There was no difference across Nocardia species in terms of history of trauma (P=0.88), agricultural work (P=0.43), age (P=0.38), gender (P=0.24), or duration of symptoms (P=0.50). N. cyriacigeorgica ulcers were associated with a vegetative matter injury (P=0.03). There were no contact lens wearers.
Nocardia spp cases had a median duration of symptoms of 10 days (IQR 4 to 15 days) versus 4 days (IQR 3 to 7 days) in non-Nocardia cases. Median enrollment BSCVA of Nocardia spp cases was 0.34 logMAR (approximate Snellen equivalent 20/45, IQR 0.1 to 1.2 logMAR (20/25 to 20/300)), compared to 0.86 logMAR (20/145, IQR 0.42 to 1.7 logMAR (20/50 to Count Fingers), P<0.001) in non-Nocardia cases. Median infiltrate/scar size at enrollment in Nocardia spp cases was 2.7 mm (IQR 1.9 to 4.1 mm), and 2.7 mm (IQR 1.9 to 4.0 mm, P=0.75) in non-Nocardia cases. Of the 55 Nocardia cases, 51 (93%) returned for their 3-month follow-up visit. At 3 months, median BSCVA in Nocardia keratitis cases was 0.12 logMAR (20/25, IQR 0.00 to 0.74 logMAR (20/20 to 20/100)), compared to 0.30 logMAR (20/40, IQR 0.06 to 0.68 logMAR (20/22 to 20/95), P=0.25) in all other organisms. Median infiltrate/scar size at 3 months was 2.7 mm (IQR 1.6 to 3.7 mm) in Nocardia cases, and 2.7 mm (IQR 1.8 to 3.9 mm, P=0.9) in non-Nocardia cases. Controlling for baseline characteristics, Nocardia spp ulcers were associated with 2 lines less improvement in 3-month BSCVA (0.21 logMAR, 95% CI 0.09 to 0.33 logMAR, P=0.001, Table 2) and 0.2 mm less improvement in infiltrate/scar size (95% CI 0.02 to 0.4 mm, P=0.03, Table 3) compared to other bacterial ulcers.
Median time to re-epithelialization in Nocardia ulcers was 5.5 days (IQR 2.5 to 14 days), compared to 7.5 days (IQR 2.5 to 16.5 days) in all other bacterial ulcers. There was no difference in time to re-epithelialization, adjusting for baseline epithelial defect size and treatment, between Nocardia spp and all other organisms (Hazards Ratio 0.82, 95% CI 0.60 to 1.12, P=0.21). One (2%) Nocardia spp case had a corneal perforation, compared to 14 of the remaining 445 other bacterial cases (3%, P>0.999). During the course of treatment, 18 patients (33%) with Nocardia keratitis had amikacin added to their treatment regimen. Of these, 9 were in the corticosteroid arm (29%) and 9 were in the placebo arm (38%, P=0.57). The median study day on which amikacin was added was 4.5 days after enrollment (IQR 1 to 9 days). Amikacin typically was added to cases that were severe. Median enrollment BSCVA was worse in patients who received amikacin, although this difference was not significant (0.46 logMAR versus 0.28 logMAR in the moxifloxacin-only group, P=0.43). Median 3-month BSCVA was worse in patients receiving amikacin (0.54 logMAR vs. 0.09 logMAR, P=0.01). Time to re-epithelialization was longer in cases that received amikacin versus those that did not (13 days versus 4 days, P=0.004). Patients who had amikacin added to their regimen had a higher median MIC to moxifloxacin than those who did not have amikacin added (12.0 μg/ml, IQR 1.50 μg/ml to 32 μg/ml versus 1.7 μg/ml, IQR 0.5 μg/ml to 4 μg/ml). Changes in medication were permitted by treated physicians by the SCUT protocol according to clinical parameters, not susceptibility.
Of the patients with Nocardia spp ulcers, 31 patients were randomized to receive topical corticosteroid and 24 were randomized to placebo (P=0.32, Fisher's exact test). At 3 months, 4 patients had been lost to follow-up, resulting in 28 patients from the corticosteroid arm and 23 patients from the placebo arm that were included. On average, the use of corticosteroids was associated with a 0.40 mm larger infiltrate/scar size at 3 months in Nocardia keratitis cases, with enrollment infiltrate/scar size and addition of amikacin as covariates (0.40 mm, 95% CI 0.03 to 0.77mm, P=0.03, Table 4). A sensitivity analysis using an interaction term (corticosteroid by Nocardia spp) did not change these results. There was no difference in 3-month BSCVA between corticosteroid and placebo arms, controlling for enrollment BSCVA and addition of amikacin (0.14 logMAR, 95% CI −0.085 to 0.37, P=0.21). There was no difference in time to re-epithelialization with the use of corticosteroids (HR 0.89, 95% CI 0.49 to 1.61, P=0.70). There was no difference in perforation between the two arms (P=1.0).
While Nocardia spp have historically been a relatively rare cause of bacterial keratitis, the incidence of Nocardia spp keratitis may be increasing, especially in India.15 Previous case series from South India have shown that Nocardia spp were responsible for a small proportion of bacterial ulcers, however in SCUT, Nocardia was the third most commonly-isolated organism.5,16 Prior reports have evaluated outcomes in Nocardia keratitis in a retrospective manner, and no information is available on the utility of corticosteroids for this type of keratitis. In this prospective subanalysis of a clinical trial, we found that Nocardia keratitis generally had good outcomes, but the use of corticosteroids resulted in larger infiltrate/scar sizes, suggesting they may not be appropriate for treating this disease. Additionally, treatment with fluoroquinolones as monotherapy in two-thirds of cases resulted in good median visual acuity (approximately 20/25), despite having variable in vitro susceptibility.
Overall, patients did not have a high degree of vision loss at enrollment (approximate Snellen equivalent 20/40), and outcome visual acuity was good (approximate Snellen equivalent 20/25). Nocardia keratitis cases had significantly less improvement at 3 months in visual outcomes and infiltrate/scar size than ulcers due to all other bacteria. This indicates that there may not have been room for dramatic improvement, as seen in ulcers of other etiologies.11 We did not find any difference in baseline characteristics or clinical outcomes across species of Nocardia. Patients with Nocardia spp ulcers had a significantly delayed presentation compared to ulcers with non-Nocardia ulcers. Despite this, infiltrate/scar size was almost identical in ulcers due to Nocardia vs. other bacterial organisms, and visual acuity was significantly better at enrollment in Nocardia ulcers. It is possible that the scars of Nocardia spp ulcers may be less opaque or dense than non-Nocardia ulcers, but this was not assessed in this study.
The use of topical corticosteroids in bacterial corneal ulcers is controversial. Corticosteroids may reduce inflammation that can lead to ocular damage, however there is a risk that they may exacerbate the infection and cause corneal melting.17–20 The primary SCUT analysis found no overall difference in safety and efficacy between adjunctive corticosteroid therapy and placebo.16 The effect of topical corticosteroids on Nocardia spp ulcers has not been previously well characterized. Case reports have suggested that topical corticosteroids may result in recurrence of the infection and prolonged healing time.21 In this study, we found that the use of adjunctive corticosteroids was associated with significantly larger infiltrate/scar sizes at 3 months in Nocardia keratitis cases. There was no difference in visual acuity, time to re-epithelialization, or perforation between the corticosteroid and placebo arms. Epithelial healing may not be an appropriate indicator for improvement in Nocardia keratitis, because the disease can progress despite epithelial defect healing. However, these findings suggest that caution should be taken when treating patients with presumed Nocardia keratitis with corticosteroids.
There have been few reports in the literature about the response of Nocardia keratitis to fluoroquinolones. In vitro studies have shown that Nocardia isolated from keratitis has variable susceptibilities to fluoroquinolones4,5, and in this study, gatifloxacin had the best activity, followed by moxifloxacin. Nearly all isolates were susceptible to amikacin. It is not clear how Nocardia keratitis responds clinically to treatment with fluoroquinolones. To date, studies of Nocardia keratitis in vivo have focused primarily on treatment with amikacin. In this study, all patients were started on moxifloxacin as the initial treatment per study protocol. Treating physicians were allowed to change or add antibiotics if they felt it was medically necessary. Approximately one third of patients had amikacin added to their moxifloxacin regimen, generally within the first week of treatment. Patients who had amikacin added to their treatment regimen had more severe ulcers at presentation, with worse visual acuity and larger infiltrate/scar sizes. They also had worse visual acuity outcomes, suggesting these are cases that were more difficult to treat. The cases that received only moxifloxacin steadily improved, but were less severe at presentation. These results suggest that for less severe Nocardia ulcers, moxifloxacin monotherapy may be a viable treatment option. However, no definitive conclusions about the efficacy of moxifloxacin for the treatment of Nocardia keratitis can be drawn from this study, as this study was not designed to compare the efficacies of amikacin and moxifloxacin.
This study must consider several limitations. While Nocardia spp was the third most commonly-isolated organism during the course of the trial, only 55 samples were isolated, resulting in a small study sample size. There was a relatively small number of each Nocardia species, making comparisons between species difficult. Due to the small sample size, we are unlikely to have detected even a moderate effect on visual acuity. However, we did find a difference in infiltrate/scar size, showing that we did have sufficient power to detect this difference. As a subanalysis of a larger clinical trial, this study may suffer a selection bias resulting from the clinical trial's exclusion criteria, such as the exclusion of ulcers with a descemetocoele. Some excluded patients may have been Nocardia spp cases; no information was collected on patients who were excluded. However, because this study was part of a prospective, randomized, controlled trial, all patients followed a standardized treatment protocol and had standardized study measurements of visual acuity, infiltrate/scar and epithelial defect size at pre-specified time points. This methodology improves our ability to make a direct comparison in this subgroup to ulcers from other organisms, and allows us to assess the utility of corticosteroids in a rigorous manner. Although the use of corticosteroids resulted in worse infiltrate scar, this did not appear to affect visual acuity. However, it is possible that high contrast acuity may not disclose an adverse effect on visual function that might be revealed by other measures such as contrast sensitivity.
In this study, Nocardia spp ulcers improved less over the course of treatment compared to ulcers of other etiologies, but Nocardia ulcers may have had less room for improvement given that they presented with better visual acuity. The use of corticosteroids was associated with a worse infiltrate/scar size at 3 months. The susceptibility of isolates to fluoroquinolones was variable; however, cases that were treated only with moxifloxacin, which were in general less severe at presentation than those where amikacin was added, had good clinical outcomes, suggesting that moxifloxacin may be an acceptable treatment for such cases. Clinical outcomes in Nocardia keratitis generally are good, but there is no evidence that corticosteroids are of benefit in ulcers due to this organism, and in fact may result in worse outcomes.
Funding/Support Funding for the Steroids for Corneal Ulcers Trial was from the National Eye Institute, U10 EY015114. Dr. Acharya is supported by a National Eye Institute K23EY017897 grant and a Research to Prevent Blindness Award. The Department of Ophthalmology at UCSF is supported by a core grant from the National Eye Institute, EY02162, an unrestricted grant from Research to Prevent Blindness, New York, NY, and That Man May See, Inc, San Francisco, CA. Alcon provided moxifloxacin (Vigamox) for the trial. The sponsors did not have a role in the design and conduct of the study; collection, management, analysis and interpretation of the data; and preparation, review or approval of the manuscript.
Other Acknowledgments: We would like thank the research staff at each of the trial sites. We are also grateful for the invaluable guidance and advice of the SCUT data and safety monitoring board: Marian Fisher, Ph.D. (chair, University of Wisconsin, Madison), Anthony Aldave, M.D. (Jules Stein Eye Institute), Donald Everett, M.A. (National Eye Institute), Jacqueline Glover, Ph.D. (University of Colorado, Denver), K. Ananda Kannan, M.D. (Tamil Nadu Dr. M.G.R. Medical University), Steven Kymes, Ph.D. (Washington University), Gudlavalleti Venkata.S. Murthy, M.D. (Indian Institute of Public Health), and Ivan Schwab, M.D. (University of California, Davis)
Prajna Lalitha, MD is currently the Chief of Ocular Microbiology Laboratory at Aravind Eye Hospital, Madurai, India. She is also a practicing Ophthalmologist at the same institute since 2002. She holds a dual degree in both Ophthalmology and Microbiology. Her main area of interest is in the field of infections of the eye. Her research focus is on understanding the host immune response in fungal corneal ulcers.
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Financial Disclosures: None of the authors have any financial disclosures to report.
Conformity with Author Information: This research received prospective Institutional Review Board approval from the University of California, San Francisco Committee on Human Research, the Aravind Eye Hospital Institutional Review Board, and the Dartmouth University Committee for the Protection of Human Subjects. Informed consent was obtained from all participants. The study was HIPAA-compliant. The Steroids for Corneal Ulcers Trial is registered with clinicaltrials.gov, NCT #00324168.
Contributions of Authors: Design of the study (PL, MS, RR, MR, JM, CEO, MEZ, SDM, TML, NRA); Conduct of the study (PL, MS, RR, MR, JM, JLP, AS, CEO, KJR, MEZ, SDM, TML, NRA); data collection (PL, MS, RR, MR, JM, JLP, CEO, MEZ, TML, NRA); management of data (PL, JLP, KJR); analysis of data (AS, CEO, KJR, NRA); interpretation of data (PL, MS, RR, MR, JM, AS, CEO, MEZ, SDM, TML, NRA); preparation of manuscript (PL, AS, CEO, NRA); review of manuscript (PL, MS, RR, MR, JM, JLP, AS, CEO, KJR, MEZ, SDM, TML, NRA); approval of manuscript (PL, MS, RR, MR, JM, JLP, AS, CEO, KJR, MEZ, SDM, TML, NRA).