Purpose
In previous studies of fungal keratitis (FK) from temperate countries, yeasts were the predominant isolates, with ocular surface disease (OSD) being the leading risk factor. Since the 2005–2006 outbreak of contact lens (CL)-associated Fusarium keratitis, there may have been a rise in CL-associated filamentary FK in the United Kingdom. This retrospective case series investigated the patterns of FK from 2007 to 2014. We compared these to 1994–2006 data from the same hospital.
Design
Retrospective observational study.
Methods
All cases of FK presenting to Moorfields Eye Hospital between 2007 and 2014 were identified. The definition of FK was either a fungal organism isolated by culture or fungal structures identified by light microscopy (LM) of scrape material, histopathology, or in vivo corneal confocal microscopy (IVCM). Main outcome measure was cases of FK per year.
Results
A total of 112 patients had confirmed FK. Median age was 47.2 years. Between 2007 and 2014, there was an increase in annual numbers of FK (Poisson regression, P = .0001). FK was confirmed using various modalities: 79 (70.5%) by positive culture, 16 (14.3%) by LM, and 61 (54.5%) by IVCM. Seventy-eight patients (69.6%) were diagnosed with filamentary fungus alone, 28 (25%) with yeast alone, and 6 (5.4%) with mixed filamentary and yeast infections. This represents an increase in the proportion of filamentary fungal infections from the pre-2007 data. Filamentary fungal and yeast infections were associated with CL use and OSD, respectively.
Conclusions
The number of FK cases has increased. This increase is due to CL-associated filamentary FK. Clinicians should be aware of these changes, which warrant epidemiologic investigations to identify modifiable risk factors.
Fungal keratitis (FK) is an important cause of infectious keratitis and ocular morbidity worldwide. The clinical diagnosis of FK can be difficult or may not initially be considered, resulting in delayed treatment. The available drugs have variable impact and in nonresponsive cases, surgical excision of the infected cornea is required to control the infection. Moreover, visual outcomes of FK are often worse than for bacterial keratitis.
In tropical countries, fungi account for up to 67% of corneal infections. Filamentary fungi associated with trauma cause the majority of these infections. This has also been reported in regions with subtropical climates. In contrast, FK is a relatively rare clinical problem in temperate countries such as the United Kingdom (UK). A 2-year (2003–2005) national surveillance study in the UK estimated a minimum average incidence of FK at 0.32 (95% confidence interval [CI] 0.24–0.44) cases per million individuals per year. In that study, 23 of 39 (57.5%) were yeast (candida) infections and 17 of 39 (42.5%) were filamentary fungal infections. The majority of FK cases (25/39, 63.2%) were associated with ocular surface disease (OSD). This association was particularly strong for yeast infections, which all had OSD. Trauma was associated with 11 of 39 (29%) and contact lens (CL) use was reported in only 3 of 39 cases (7.9%), which were all filamentary. This was consistent with reports of FK in other high-income countries with temperate climates. An earlier study from Moorfields Eye Hospital, a large ophthalmic hospital serving London and southeast England, reported on FK presenting over a 13-year period (1994–2006). During that time, yeast infections accounted for the majority of FK cases and were strongly associated with OSD. During the same period CL-associated filamentary fungal keratitis was relatively uncommon.
In 2005–2006, there was an outbreak of Fusarium keratitis in CL users, reported in the United States, Singapore, Hong Kong, Europe, and the French West Indies. Cases were thought to be associated with the use of the ReNu with MoistureLoc (Bausch & Lomb, alexidine dihydrochloride 0.00045%) CL disinfection solution. Since this solution has been globally recalled on May 15, 2006, the incidence may have reduced. However, the perception among clinicians in the UK is that the number of FK cases has increased again in recent years, with proportionately more CL-associated filamentary fungi. To investigate this we conducted a retrospective study of all confirmed cases of FK presenting to Moorfields Eye Hospital from 2007 to 2014. We also compared these data with data collected from the same institution between 1994 and 2006.
Methods
This study was a retrospective review of medical records. The protocol was approved by the Moorfields Eye Hospital Clinical Research Management and Audit Department (reference: CA13/CED/12). The study adhered to the tenets of the Declaration of Helsinki.
Case Ascertainment
To identify cases we made the assumption that all cases of fungal keratitis (suspected or confirmed) would be commenced on topical antifungal treatment. We queried the hospital pharmacy database for the record numbers of all patients who were dispensed any antifungal treatment between January 1, 2007 and December 31, 2014. The medical notes were retrieved and reviewed to ascertain whether the individual met the case definition for inclusion in this study.
Case Definition
For the purpose of this study we considered an individual with clinical features of suppurative keratitis to be a case of FK if the individual met 1 or more of the following criteria: (1) a fungal organism grown from a corneal scrape or biopsy sample on 1 or more culture media; (2) fungal elements present in light microscopy of a corneal scrape sample; (3) fungal elements present in histopathology of corneal biopsy tissue; (4) fungal elements identified by in vivo confocal microscopy (IVCM).
Data Collection
Data collected from the medical record included: demographic information, country where FK was acquired, potential risk factors (such as CL use, topical steroid use, trauma), past ophthalmic history, microbiology results, IVCM results, and visual acuity outcome. The presenting visual acuity (VA) was routinely measured with a Snellen chart at 6 meters, with spectacle correction if available. The OSD group included patients with dry eyes, corneal exposure, blepharitis, persistent epithelial defects, or chronic ocular surface inflammatory conditions (eg, atopic keratoconjunctivitis, mucous membrane pemphigoid, Stevens-Johnson syndrome).
Laboratory Investigations
At Moorfields, specimens for culture are typically obtained by scraping the base and edges of corneal ulcers with a sterile, disposable 23 gauge needle. Samples are smeared on a glass slide and stained for microscopy. Samples are also inoculated onto a minimum of blood agar and Sabouraud dextrose agar. In addition, several other media are also frequently used: Robertson’s cooked meat broth, brain-heart infusion, and non-nutrient agar. All solid media are incubated at 37 C for a minimum of 1 week. Broths are usually cultured for 2 days and are then subcultured on solid media for a minimum of 1 week. All microbiological investigations were undertaken independently in an external laboratory and cultured isolates are sent to the UK Mycology Reference Laboratory for speciation. For biopsies, a superficial lamellar disc of affected cornea was taken under local anesthesia and sent for microbiological and histopathologic staining. Specimens from biopsy or keratoplasty material were cultured from homogenized tissue. The use of a panfungal polymerase chain reaction (PCR) assay only entered our routine practice during the last 24 months of the period studied. Therefore, for consistency throughout the 2007–2014 study period it was not used as an inclusion criterion for FK.
In Vivo Confocal Microscopy
IVCM was performed and interpreted by experienced clinicians using the HRT II/RCM confocal microscope (Heidelberg Engineering, Dossenheim, Germany). Typically, the ulcer is systematically surveyed around its circumference and more centrally at variable depths to assess different levels of the cornea. Volume scans of areas of interest were captured and stored for analysis.
Statistical Analysis
Data were managed in Access (Microsoft) and analyzed using STATA 13 (StataCorp LP, Texas, USA). Differences in the distribution of categorical variables between groups were analyzed using the χ 2 test or logistic regression. For continuous variables, differences in distribution between groups were analyzed by the Mann-Whitney test. Poisson regression was used to analyze change in presentation rates. Multivariable logistic regression was used to investigate risk factors for filamentary vs yeast infection. Variables with significant associations on univariable analyses at a level of P < .05 were included in the initial multivariable analysis. Nonsignificant terms were then removed from the multivariable model in a step-wise manner, with only those with P < .05 being retained.
To assess longer-term trends we compared the 2007–2014 data with data collected and previously reported from the same hospital during the preceding 13 years (1994–2006). This is a subset of the previously reported data that only includes whole calendar years. The 1994–2006 series had more restricted inclusion criteria, as it only included cases that were both UK-acquired and culture positive. It pre-dated the routine use of IVCM. To compare data from the 2007–2014 series with the 1994–2006 series, we excluded cases in the 2007–2014 series that were acquired outside the UK or did not have a positive culture.
Results
Patient Characteristics
Between January 1, 2007 and December 31, 2014, 200 patients were prescribed an antifungal treatment for suspected FK. Of these, 112 patients met the study inclusion criteria for FK, representing an average of 14 cases per year. Of the 88 patients who were started on antifungal treatment but did not meet the inclusion criteria for confirmed FK, 30 received continued empirical treatment for fungal keratitis, 24 received continued treatment for a microbial keratitis of unspecified cause, 29 were diagnosed with bacterial keratitis, 3 were diagnosed with herpetic keratitis, 1 was diagnosed with mycobacterium keratitis, and 1 was diagnosed with a rheumatoid corneal melt.
All patients had unilateral infections. Their median age was 47.2 years, and 46/112 (41.1%) were male ( Table 1 ). The majority of cases were acquired in the UK (91/112 [81.3%]), largely from London and the east and the southeast of England ( Table 2 ). Of the 112 cases, 21 were acquired outside the UK: 5/112 (4.5%) in other European countries, 3/112 (2.7%) in African countries, 7/112 (6.2%) in Asia, and 6/112 (5.4%) in the Americas ( Table 2 ). Overall, there was strong evidence of an increase in the total annual number of cases presenting during the 2007–2014 period (Poisson regression, P = .0001, Figure 1 , Upper left). When individuals who acquired their infections outside the UK are excluded from this analysis, there was still strong evidence of an increase in the annual number of cases (Poisson regression, P = .0001, Figure 1 , Upper left). There was no evidence of an increase in the number of infections acquired outside the UK during the 2007–2014 period (Poisson regression, P = .6, Figure 1 , Upper left).
| Variables | Filamentary | Yeast | Mixed | All |
|---|---|---|---|---|
| 78 (%) | 28 (%) | 6 (%) | 112 (%) | |
| Age, median (IQR) a | 45.7 (31–56) | 49.9 (44–66) | 48.6 (28–56) | 47.2 (36–57) |
| Male sex b | 32 (41.0%) | 13 (46.4%) | 1 (16.7%) | 46 (41.1%) |
| Risk factors | ||||
| Contact lens | 52 (66.7%) | 7 (25.0%) | 5 (83.3%) | 64 (57.1%) |
| OSD | 8 (10.3%) | 16 (57.1%) | 1 (16.7%) | 25 (22.3%) |
| Ocular surgery | 11 (14.1%) | 14 (50.0%) | 0 | 25 (22.3%) |
| Trauma | 9 (11.5%) | 4 (14.3%) | 0 | 13 (11.6%) |
| Prior steroid use | 17 (21.8%) | 17 (60.7%) | 2 (33.3%) | 36 (32.1%) |
| Presenting VA (n = 111) c | ||||
| 6/5–6/12 | 14 (18.0%) | 2 (7.4%) | 2 (33.3%) | 18 (16.2%) |
| 6/18–6/60 | 30 (38.5%) | 5 (18.5%) | 4 (66.6%) | 39 (35.1%) |
| ≤ CF | 34 (43.6%) | 20 (74.1%) | 0 | 54 (48.7%) |
| Final best-corrected VA (n = 106) d | ||||
| 6/5–6/12 | 47 (61.8%) | 7 (29.2%) | 5 (83.3%) | 59 (55.7%) |
| 6/18–6/60 | 18 (23.7%) | 7 (29.2%) | 1 (16.7%) | 26 (24.5%) |
| ≤ CF | 11 (14.5%) | 10 (41.7%) | 0 | 21 (19.8%) |
a Mann-Whitney test, for the comparison of filamentary and yeast infections: P = .051.
b χ 2 test, for the comparison of filamentary and yeast infections for sex: P = .6.
c χ 2 test, for the comparison of filamentary and yeast infections for presenting VA: P = .024; presenting vision was not available in one individual with learning disability.
d χ 2 test, for the comparison of filamentary and yeast infections for final VA: P = .006; final best-corrected VA were only available in 106 individuals (6 individuals were lost to follow-up).
| Regions/Countries | n/112 (%) |
|---|---|
| United Kingdom | 91 (81.3%) |
| Greater London | 58 (63.7%) a |
| East of England | 17 (18.7%) a |
| Southeast England | 9 (9.9%) a |
| Southwest England | 3 (3.3%) a |
| West Midlands | 3 (3.3%) a |
| Northwest England | 1 (1.1%) a |
| Europe | |
| Malta | 1 (0.9%) |
| Cyprus | 1 (0.9%) |
| Spain | 2 (1.8%) |
| Poland | 1 (0.9%) |
| Americas | |
| North America (Florida) | 1 (0.9%) |
| Costa Rica | 1 (0.9%) |
| Jamaica | 1 (0.9%) |
| Ecuador | 1 (0.9%) |
| Brazil | 1 (0.9%) |
| Venezuela | 1 (0.9%) |
| Asia | |
| China | 1 (0.9%) |
| India | 2 (1.8%) |
| Bangladesh | 1 (0.9%) |
| Indonesia | 1 (0.9%) |
| Vietnam | 1 (0.9%) |
| Cambodia | 1 (0.9%) |
| Africa | |
| Gambia | 1 (0.9%) |
| Nigeria | 1 (0.9%) |
| Algeria | 1 (0.9%) |
a For UK regions the % values are calculated out of all 91 cases acquired in the UK.
Diagnostic Modality
Figure 2 illustrates the diagnostic modality by which the FK diagnosis was made for the 112 cases. There was a positive culture in 79 patients: 73/112 (65.2%) from corneal scrapings, 6/112 (5.4%) from corneal biopsy culture. One was culture positive from both corneal scraping and biopsy samples. There was 1 case in which the presence of fungal hyphae was only confirmed by histopathology of the corneal button (biopsy) removed following a penetrating keratoplasty. In 16 of the 112 patients (14.3%), fungal hyphae or yeasts were identified by light microscopy; 4 of these were by light microscopy alone. IVCM was performed for 80/112 patients (71.4%); of those, fungal structures were identified in 61 (76.3%). In 28 patients the diagnosis of FK was only made with IVCM (ie, negative on light microscopy, biopsy histology, and culture). A total of 28 cases were tested by panfungal PCR. Six were positive by PCR. Of these, 4 were also positive by both culture and IVCM, 1 was also positive by IVCM, and 1 was also positive by culture. No cases of FK were detected by PCR alone.
Microbiological Diagnosis
Overall, 78 of the 112 cases (69.6%) were filamentary fungal infections, 28 of 112 (25.0%) were yeast infections, and 6 of 112 (5.4%) mixed filamentary and yeast infections. There was no evidence of a difference in the pattern of organisms between those acquired in the UK and those acquired outside the UK ( P = .7). There was evidence (Poisson regression, P = .005, Figure 1 , Upper right) of an increase in the absolute numbers of cases presenting attributable to filamentary fungi acquired in the UK. However, there was no evidence of such an increase in the number of yeast cases acquired in the UK (Poisson regression, P = .3, Figure 1 , Upper right), or of an increase in the numbers of filamentary fungi acquired outside the UK (Poisson regression, P = .9, Figure 1 , Upper right). This suggests that it is the increase in the absolute numbers of filamentary fungi acquired in the UK that is driving the increase in the overall number of FK cases being presented. There was no evidence of a difference in the sex distribution between filamentary fungal and yeast infections ( P = .6), Table 1 . The median age of people with yeast infections was slightly higher than in filamentary cases; however, this was not statistically significant ( P = .051, Figure 1 , Middle left). Of the 61 cases identified by IVCM, 58 had branching filamentary hyphae (of which 27 were culture positive for filamentary fungi) and 3 had large round bodies consistent with a diagnosis of yeast (of which 1 was culture positive for Candida spp) ( Figure 3 ).
There were 90 fungal culture isolates ( Table 3 ) from the 79 culture-positive cases. In 11 cases 2 fungal organisms were co-cultured: 7 grew 2 different filamentary organisms and 4 grew a filamentary organism and a yeast. Overall, 30/90 isolates (33.3%) were yeasts and 60/90 (66.7%) were filamentary fungi. Fusarium spp were the commonest filamentary fungi isolated (33/79 cases, 41.8%), followed by Aspergillus spp (9/79 cases, 11.4%). All the yeast isolates were subspecies of Candida (30/79 cases, 38.0%). Bacterial co-infection was present in 20 of the 112 cases (17.9%) ( Table 4 ). In 1 case Acanthamoeba was also co-cultured. There was no evidence of a difference in the proportion of filamentary and yeast cases that had a bacterial co-infection ( P = .5).
| Fungal Species | n/79 (%) |
|---|---|
| One filamentary fungal isolate | |
| Fusarium sp | 26 (32.9%) |
| Aspergillus sp | 7 (8.9%) |
| Scopulariopsis brevicaulis | 1 (1.3%) |
| Acremonium | 2 (2.5%) |
| Paecilomyces | 1 (1.3%) |
| Rhizomucor | 1 (1.3%) |
| Scedosporium apiospermum | 1 (1.3%) |
| Cladosporium | 1 (1.3%) |
| Curvelaria | 1 (1.3%) |
| Species not defined | 1 (1.3%) |
| Subtotal | 42 (53.2%) |
| Two filamentary fungal isolates | |
| Fusarium sp + Acremonieum | 2 (2.5%) |
| Fusarium sp + Gibberella fujikuroi | 1 (1.3%) |
| Fusarium sp + Purpureocillium lilacinum | 1 (1.3%) |
| Fusarium sp + Scedosporium apiospermum | 1 (1.3%) |
| Aspergillus sp + Chrysosporium | 1 (1.3%) |
| Aspergillus sp + Scedosporium apiospermum | 1 (1.3%) |
| Subtotal | 7 (8.9%) |
| Yeasts only | |
| Candida sp | 26 (32.9%) |
| Subtotal | 26 (32.9%) |
| Yeast and filamentary fungal isolates | |
| Candida sp + Fusarium sp | 2 (2.5%) |
| Candida sp + Paecilomyces | 1 (1.3%) |
| Candida sp + Achromobacter xylosoxidans | 1 (1.3%) |
| Subtotal | 4 (5.2%) |
| Total | 79 (100%) |
| Microorganism | n/112 Percentage (%) |
|---|---|
| Gram-positive bacteria | |
| Coagulase-negative staphylococcus | 7 (6.3%) |
| Staphylococcus epidermidis | 2 (1.8%) |
| Staphyloccous aureus | 2 (1.8%) |
| Staphylococcus capitis | 1 (0.9%) |
| Corynebacterium | 1 (0.9%) |
| Microbacterium oxydans | 1 (0.9%) |
| Brevibacterium | 1 (0.9%) |
| Gram-negative bacteria | |
| Pseudomonas aeruginosa | 3 (2.7%) |
| Klebsiella | 1 (0.9%) |
| Enterococcus faecalis | 1 (0.9%) |
Clinical Course and Treatment
The presenting visual acuity was count fingers or less in 54 (48.7%) of the affected eyes ( Table 1 ). There was evidence that the presenting vision was worse among the cases with yeast infection ( P = .024). Visions at final follow-up were available in 106 individuals. By the final follow-up there was an improvement in the vision of 74/106 eyes (69.8%), no change in 16/106 (15.1%), and a deterioration in 16/106 (15.1%). The number of eyes with a visual acuity of count fingers or less was 21 (20.0%) at the final follow-up. There was no evidence to suggest that final visual acuities of patients diagnosed by positive cultures compared with patients who had negative cultures (diagnosed by other modalities) were different ( P = .50). At least 1 corneal graft procedure was performed in 34/112 cases (30.4%): 27 had a therapeutic keratoplasty, 14 had a penetrating keratoplasty, and 5 had a lamellar keratoplasty for restoration of vision. Two patients had a conjunctival flap and 4 eyes were eviscerated.
All patients were treated with topical antifungal agents. During this 8-year period there was a change in the pattern of prescribing for filamentary fungal infections ( Figure 1 , Middle right). Initially most cases were treated with econazole 1%. From 2009 there was increased use of voriconazole 1%. From 2013 onward there was a move away from voriconazole 1%, to natamycin 5%. Yeast infections were usually treated with topical amphotericin 0.015% or voriconazole 1%. One or more oral antifungal agents were used in 65/112 cases (58%): voriconazole in 48/112 (42.9%), itraconazole in 14/112 (12.5%), and fluconazole in 10/112 (8.9%).
Risk Factors
Several potential risk factors were reported, including contact lens use, OSD, prior ocular surgery, and a history of trauma ( Table 1 ). Evidence for the associations between the class of fungus isolated (yeast or filamentary) and each of these risk factors for infection are shown in Table 5 . The use of contact lenses at the time of onset of symptoms was reported by 64 of 112 individuals (57.1%) ( Table 1 ). There was evidence that filamentary fungal infections were more frequently associated with contact lens use than were yeast infections ( Table 5 ). The types of contact lens used were: soft (for vision), 56/64 (87.5%); therapeutic (bandage), 3/64 (4.7%); and rigid gas-permeable, 4/64 (6.3%). The type of contact lens used was not recorded in one individual. Among the 56 wearing soft (for vision) contact lenses, 11 (19.6%) used daily disposable, 17 (30.4%) used fortnightly disposable, and 25 (44.6%) used monthly disposable. The pattern of wear of contact lenses was not recorded in 3 patients. Although the data on “risk” behavior were not systematically collected, of the soft (for vision) CL users, 4/56 (7.1%) reported overnight use, 9/56 (16.1%) reported swimming in lenses, and 11/56 (19.6%) reported showering in lenses. All 3 cases associated with the use of therapeutic CL had OSD. These lenses were being used for up to 1 month between lens changes.
