|Year : 2018 | Volume
| Issue : 3 | Page : 213-219
The epidemiology of nonviral microbial keratitis in a tertiary care center in Muscat, Oman
Alyaqdhan Al-Ghafri, Abdullatif Al-Raisi
Department of Ophthalmology, Al-Nahdah Hospital, Muscat, Oman
|Date of Web Publication||29-Oct-2018|
Department of Ophthalmology, Al-Nahdha Hospital, Muscat
Source of Support: None, Conflict of Interest: None
| Abstract|| |
OBJECTIVE: The objective of this study is to describe the epidemiology, risk factors, etiology, and outcome of microbial keratitis in a tertiary care center in Muscat, Oman.
METHODS: The electronic records of all patients diagnosed with keratitis or corneal ulcer between January 2013 and January 2016 in Al-Nahdha Hospital were retrospectively reviewed. Patients who presented with a corneal ulcer requiring admission and who underwent culture and sensitivity studies were included in the study. Patients with viral keratitis or sterile corneal ulcers were excluded from the study.
RESULTS: A total of 606 electronic medical records of all presumed microbial keratitis were reviewed. Out of these, 304 met the eligibility criteria. The mean age of patients was 52.2 years (standard deviation [SD]: ±23.2 years; range: 0.1–89 years). A total of 198 (65%) microbial cultures yielded positive results. Of these, 182 (92%) were bacterial, 13 (7%) were fungal, and 3 (1%) cases were due to a combined (bacterial and fungal) etiology. Gram-positive bacteria accounted for 102 (55.1%), of which the majority was due to Streptococcus pneumoniae. Gram-negative bacteria accounted for 77 (41.6%) cases; half were caused by Pseudomonas aeruginosa. Keratitis in patients aged 18 years and younger was more likely to be associated with trauma (48.3%, P < 0.001) in young adults with contact lens wear (64%, P < 0.001) and in adults over 40 years with blepharitis (55.6%), sequelae of previous trachoma infection (26.3%), and eyelid abnormalities (18.4%). Following recovery, corneal scarring was seen in 63.2% of patients.
CONCLUSION: Microbial keratitis affects patients of all age groups but is more common in older adults. The vast majority of culture-proven cases are due to bacterial infections. Children and teenagers are more likely to develop keratitis following eye trauma whereas young adults mostly develop the condition in association with contact lens wear. Ocular surface disease is the most important risk factor in older adults. The majority of patients end up with corneal scarring.
Keywords: Contact lens-related keratitis, corneal ulcer, microbial keratitis, ocular surface disease
|How to cite this article:|
Al-Ghafri A, Al-Raisi A. The epidemiology of nonviral microbial keratitis in a tertiary care center in Muscat, Oman. Oman J Ophthalmol 2018;11:213-9
|How to cite this URL:|
Al-Ghafri A, Al-Raisi A. The epidemiology of nonviral microbial keratitis in a tertiary care center in Muscat, Oman. Oman J Ophthalmol [serial online] 2018 [cited 2019 Oct 16];11:213-9. Available from: http://www.ojoonline.org/text.asp?2018/11/3/213/244330
| Introduction|| |
Microbial keratitis is a serious yet preventable cause of visual impairment. The condition can be due to a bacterial, fungal, acanthamoeba, or viral infection of the cornea.
Several predisposing factors are implicated in microbial keratitis, which differ in frequency between countries. While contact lens wear was found to be the most significant risk factor in industrialized countries, trauma and ocular surface disease seem to be more common in developing nations.
Likewise, there is variability in the profile of causative organisms between countries. Studies from developed countries reported bacterial infections as the most common etiology, whereas fungal infections were more prevalent in areas with higher population of agricultural workers due to increased risk of trauma by vegetable matter.
In this case series, we describe the epidemiology, risk factors, microbiological profile, and outcome of microbial keratitis in a tertiary hospital in Muscat, Oman.
| Methods|| |
In this case series, we reviewed the electronic records of all patients admitted with a working diagnosis of microbial keratitis between January 2013 and January 2016 to Al-Nahdha Hospital, a tertiary care hospital and the main ophthalmic referral center in the country. Microbial keratitis was defined as corneal infiltrates with or without an epithelial defect and with or without signs of suppuration. Of note, it is the hospital policy to admit all cases presenting with suspected microbial keratitis for inpatient management.
All patients with signs of microbial keratitis undergo culture and sensitivity studies including corneal scraping with disposable no. 15 blades for gram stain, potassium hydroxide preparation, and inoculation in blood, chocolate, Sabouraud, and MacConkey agars and addition to brain–heart infusion broth. Moreover, all contact lens wearers undergo additional culture and sensitivity testing of their contact lenses and their containers.
Patients who presented with a corneal ulcer requiring admission for treatment with fortified antibiotics and who underwent culture and sensitivity studies were included in the study. We excluded all patients with sterile ulcers including peripheral ulcerative keratitis, Mooren's ulcers, marginal keratitis, and shield ulcers and cases of viral keratitis.
Demographic data of all patients were recorded in data collection sheets, which included information about ulcer size, side, duration since onset, ocular comorbidities and risk factors, culture results, visual acuity on admission and after discharge, and outcome.
Ethical approval was obtained from Al-Nahdha Hospital Ethical Committee.
Descriptive statistics were mostly used in the study. Chi-square test was used to analyze some of the variables where an association was anticipated, such as the relationship between age groups and risk factors. All statistical methods were carried out on SPSS version 22 software (IBM®, New York, United States).
| Results|| |
A total of 606 electronic patient records were reviewed. Of these, 304 met the inclusion criteria. Females were slightly more in number than males, at 171 (56%) and 133 (44%) patients, respectively. Both right and left eyes were affected to the same extent. The mean age at presentation was 52.2 (median: 59.0, standard deviation: 23.2, range: 0.1–89 years, interquartile range: 40.0) with the majority of patients falling in the 50–85 years' age group. A smaller, but notable, rise of prevalence was between 20 and 30 years of age [Figure 1]. The majority of patients had a presenting visual acuity of 6/60 or worse. [Table 1] outlines patients' characteristics and the time from onset of symptoms till presentation.
The incidence was variable throughout the year in the 3 years of study. However, the number of cases gradually increased from 73 cases in 2013 to 98 cases in 2014, up to 133 cases in 2015 [Figure 2].
Out of all patients, 165 (54.3%) had blepharitis, making it the most frequent risk factor. History of trachoma was the second most significant risk factor, at 26.3% of all cases, as noted in patients' history or findings of trachoma sequelae on examination. This was followed by eyelid abnormalities, which included ectropion, entropion and trichiasis, contact lens wear, climatic droplet keratopathy, and trauma [Figure 3].
|Figure 3: Prevalence of predisposing factors and their distribution among age groups|
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Out of all patients with blepharitis, 156 (94.5%) patients were above 40 years of age. All patients with trachoma sequelae and almost all patients with eyelid abnormalities and climatic droplet keratopathy were in the same age group.
Fourteen (38.9%) and 17 (47.2%) patients in the “younger than 18” and “older than 40” age groups, respectively, presented with keratitis following corneal injury.
This makes trauma the most significant risk factor in patients <18 years old, affecting 48.3% (P < 0.001) of all patients in this age group [Figure 4]a. Similarly, 41 patients (78.8%; P < 0.001) with contact lens-related keratitis were in 19–40 years' age group, and only 5 patients were younger than 18 and 6 patients older than 40 years old. Contact lens-related keratitis accounted for 64.1% (P < 0.001) of all keratitis cases in 19–40 years' age group [Figure 4]b.
|Figure 4: (a) Percentage of trauma as a predisposing factor within each age group. (b) Percentage of contact lens-related keratitis within each age group|
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All cases enrolled in the study had culture and sensitivity testing. Out of these, 198 (65.1%) yielded positive culture results. Of these, 182 (91.9%) cases were due to bacterial infection, 13 (6.6%) cases were fungal, and 3 cases revealed mixed bacterial and fungal isolates. The cases caused by bacteria were mostly due to Gram-positive bacteria (102 cases, 55.1%), followed by Gram-negative bacteria (77 cases, 41.6%), 5 cases due to mixed Gram-positive and Gram-negative bacteria, and a single case of acid-fast bacteria following refractive surgery.
All cases enrolled in the study had culture and sensitivity testing. Out of these, 198 (65.1%) yielded positive culture results. Of these, 182 (91.9%) cases were due to bacterial infection, 13 (6.6%) cases were fungal, and 3 cases revealed mixed bacterial and fungal isolates. The cases caused by bacteria were mostly due to Gram-positive bacteria (102 cases, 55.1%), followed by Gram-negative bacteria (77 cases, 41.6%), 5 cases due to mixed Gram-positive and Gram-negative bacteria, and a single case of acid-fast bacteria following refractive surgery. [Table 2] outlines the microbial isolates.
|Table 2: Number of microbial isolates from the culture and sensitivity studies|
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S. pneumoniae was the most frequently isolated Gram-positive bacteria accounting for 42% of all isolates in this group, whereas P. aeruginosa was the most common in the Gram-negative group accounting for half of all Gram-negative bacteria. Out of the 16 fungal keratitis cases, Aspergillus species were most frequently isolated, affecting 7 cases (43.8%).
In patients with contact lens-related keratitis, Gram-negative bacteria were most frequently isolated, accounting for 40 out of the 43 cases (93.0%) that yielded positive culture results [Table 3]. Thirty-three of these (82.5%) were due to P. aeruginosa.
Corneal scarring was the most frequent complication (192, 63.2%). Sixteen patients required therapeutic keratoplasty, 5 cases due to corneal perforation and 11 cases for nonhealing ulcers. Seven cases out of those requiring therapeutic keratoplasty (43.8%) were due to fungal infection. Five of those had pure fungal isolates whereas two cases had mixed fungal and bacterial isolates (P < 0.001). [Table 4] shows the correlation between outcomes and pathogens. There were a total of 12 cases that ended up with corneal perforation; seven were treated with cyanoacrylate glue application and the rest with keratoplasty. Nine cases with active keratitis required evisceration, either due to endophthalmitis or intractable pain in eyes with preexisting blindness. [Table 5] outlines the complications in this cohort.
| Discussion|| |
Microbial keratitis is a serious ophthalmic emergency that may lead to devastating outcome if left untreated or if the treatment is delayed. While it may result from an unpredictable cause such as trauma, it is preventable in many instances with proper eye care, especially in patients with ocular surface disease.
There is a degree of regional variability in predisposing factors and causative pathogens, and hence, the empirical treatment should be tailored to each regional setting as per existing data. The available data on microbial keratitis in Muscat, Oman, are limited; thus, we sought to expand the knowledge on the topic through this study.
Although the condition may present at any age, our data showed two peaks of prevalence according to the age groups of 20 years and over the age of 50 years. This coincides with increased prevalence of contact lens use and ocular surface disease in each age group, respectively.
There are not many reports that outline seasonal variability of microbial keratitis. Nonetheless, the few reports that investigated the subject observed specific trends of incidence in different seasons. A study from Pennsylvania reported increased incidence during spring and decreased incidence during winter. In South India, fungal keratitis peaked in July and January, but no significant trend was observed in bacterial keratitis. In France, severe keratitis occurred more in periods of heat waves during summer time. To the contrary, we found no significant seasonal variability in the incidence of the disease throughout the years of study.
Several predisposing factors are implicated in microbial keratitis, which differ in frequency between countries. While contact lens wear was found to be the most common risk factor in industrialized countries, trauma and ocular surface disease seem to be more significant in developing nations. Contact lens wear accounted for 50.3% of bacterial keratitis cases in a study from Paris, 44.3% and 31.4% in Taiwan,, and 42.7% in Hong Kong, whereas studies from Thailand, India,, and Pakistan reported trauma as the main predisposing factor.
In our study population, ocular surface conditions, such as blepharitis, trachoma sequelae including eyelid abnormalities, climatic droplet keratopathy, and dry eye were by far the most common risk factor in general and in older patients in particular. “Dry eyes” or “dry eye syndrome” were specifically documented in 19 patient records only although anecdotal evidence from the same center where this study was conducted shows a much higher prevalence. This is likely due to under-reporting of dry eye syndrome since it is very common, especially in elderly population, and it is viewed as a nonserious condition. Keratitis in patients aged 18 years and younger was more likely to be associated with trauma (48.3%) and in young adults with contact lens wear (64%). In contrast, two studies from South Sharqiyah, Oman, reported postoperative state and climatic droplet keratopathy as the most important risk factors in general, whereas indiscriminate use of topical steroids and trauma were significant risks for developing fungal keratitis.,
Scraping of the corneal ulcer for culture and sensitivity is utilized to best isolate the causative organism in order to guide the treatment. However, the culture yield is not always high. This is most likely due to the fact that many patients begin using treatment, either pharmacological or traditional, before presenting to the ophthalmic services. The culture yield in our setting was 65.1% (i.e., positive culture in 198 out of 304 cases). This is slightly higher than some other settings around the world, which ranged from 59.3% of all samples in a study from Ahmedabad, 57.4% in Toronto, 38% in Mexico, to only 25.6% in Thailand.
Likewise, there is variability in the profile of causative organisms between countries. Studies from developed countries reported bacterial infections as the most common etiology, whereas fungal infections were more likely to occur in areas with higher population of agricultural workers due to increased risk of trauma by vegetable matter. This study showed that Gram-positive bacteria were slightly more frequent than Gram-negative bacteria at 55.1% and 41.6%, respectively. S. pneumoniae accounted for the majority of Gram-positive bacteria (42%), while P. aeruginosa accounted for half of Gram-negative bacterial cases, making it the most common Gram-negative organism in this cohort. Bacterial etiology was also the most common cause in reports from Los Angeles, Toronto, and Mexico, while both bacterial and fungal keratitides were equally common in Thailand.
It should be noted that significant variability might exist within a single county. For example, in the study from South India by Lin et al., fungal infections accounted for 63% of all cases of microbial keratitis, while bacterial etiology resulted in only 35.7%. To the contrary, 65.1% and 34.9% were the proportions of bacterial and fungal infections, respectively, in a study from Ahmadabad in western India.
The outcome of microbial keratitis depends on the type of causative organism, the preexisting ocular status, and the timing of presentation and starting of treatment. Complications include corneal scarring, corneal perforation, and endophthalmitis. A patient may require therapeutic keratoplasty if the infection is refractory to medical treatment or optical keratoplasty if visually significant scarring occurred after resolution of infection. Evisceration may be a last resort if endophthalmitis develops and the eye can no longer be salvaged.
Corneal scarring occurred in a significant proportion (63.2%) of our cohort. Sixteen patients (5.3%) required therapeutic corneal graft. In about half of there, cultures isolated fungal pathogens. This likely due to the prolonged course and poor response to treatment showed by fungal keratitis. Therapeutic corneal graft was indicated for corneal perforation in 5 cases and for a nonhealing ulcer in the remaining 11 cases.
As with most retrospective studies, missing data are a limitation in this study. This is mostly due to incomplete documentation of patients' data in the records. For this reason, a number of variables with significant missing data were not included in the analysis. It is difficult to ascertain how many of the predisposing factors were not charted in patients' records. Hence, the reported frequencies may not accurately represent the true prevalence of these factors. This is mostly true for subtle signs (e.g., dry eye syndrome) or common ones (e.g., trachoma sequelae), which are sometimes not documented by the ophthalmologists. On analyzing predisposing factors (e.g., blepharitis and dry eyes), it was not possible to assume that factors, which are missing from patients' records, are truly absent. Therefore, we did not include these in the analysis. To the contrary, factors that are due to significant events (e.g., trauma and contact lens wear) were presumed to had had always been documented whenever present, and it may be safe to assume that the absence of documentation correlates with the absence of the predisposing factor. Thus, they were included in the analysis for statistical significance. The same applies to correlating the causative organisms to the outcomes. Outcomes such as evisceration, corneal perforation, endophthalmitis, and therapeutic corneal graft are too significant to be omitted in patients' records. Accordingly, their absence from records was considered a true absence.
| Conclusion|| |
Microbial keratitis affects patients of all age groups but is more common in older adults. The vast majority of culture-proven cases are due to bacterial infections, of which most are Gram positive. Risk factors differ between age groups; children and teenagers are more likely to develop keratitis following eye trauma whereas young adults mostly develop the condition in association with contact lens wear. Ocular surface disease is the most important risk factor in older adults. Special attention should be given to elderly patients with ocular surface disease, and any eyelid abnormalities and dry eye disease should be effectively diagnosed and treated. We advise that all patients with signs of a previous trachoma infection to be put on lubricating drops for both the eyes indefinitely.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]