Infective keratitis is still one of the leading causes of blindness especially in developing countries like India. Although both bacteria and fungus are known to cause infective keratitis, the etiological agents vary from region to region depending upon geographical area depending on environmental conditions.¹⁴

In the present study, male subjects were more affected than the female which is in accordance with the study conducted by Tewari et al. in India (Table 1).¹⁵ However, there is a study in China that has reported women as predominantly affected by gender.¹⁶ This could be due to the higher employability of women particularly in the agricultural sector in China, while in India, it is males who work in the agriculture sector.

Table (1):
Epidemiological characteristics of patients.

In the present study, corneal ulceration was seen in all age groups with preponderance among the age group 41-50 years of age followed by 51-60 years (Table 1). In the results of studies conducted by Cameron et al.¹⁷ and Das et al. in Kolkata,¹⁸ 41-60 years was the predominant age group affected by this disease. This could be because this age group is actively engaged in outdoor activities and work.

There was a higher incidence of keratitis among farmers (40.5%) in this study (Table 1). This is in accordance with studies conducted by Tewari et al.¹⁵ and Suwal et al.¹⁹ but Ranjini et al. in their study reported a higher incidence of keratitis in housewives.²⁰

In this study, agriculture workers were affected more than the general population (Table 1). This is attributed to the fact that those working in agricultural fields are more prone to vegetative trauma. In northern states of India, the harvesting period is from April to mid-September. In present study, a maximum number of cases and culture positivity were seen from June–September, which happens to be the harvesting season in North India (Table 2). However, a study conducted by Krishna et al.²¹ reported a maximum number of cases during the month of January, February and June which happens to be harvesting months in South India.

Table (2):
Month wise distribution of cases and culture positive cases.

Trauma was the most common predisposing factor matching other studies conducted in South India by Ranjini et al.²⁰ but in other countries like Barhaim in the Middle East, a study conducted by Yusuf et al.²² reported wearing of contact lenses as the major risk for developing corneal ulcers. In our study, none of the patients with keratitis wore lenses. (Figure 1)

Table (3):
Distribution of isolates.

In the present study, out of 193 cases, 83 (43%) were culture positive. In culture positive samples, fungi (66.3 %) were recovered more frequently than bacteria (33.7%) (Table 3 and 4). Srinivasan et al.²³ reported an almost equal number of bacterial (47.1%) and fungal (46.8%) etiological agents with 5.1 % of mixed infection in their study. A comparison of prevalence rates of etiological agents of microbial keratitis reported in various studies, with the present study is shown in Table 5.

Table (4):
Antibiotic Sensitivity pattern of Bacterial isolates.

P: Penicillin, OX: Oxacillin CIP: Ciprofloxacin, LEV: Levofloxacin, LZ: Linezolid, VA: Vancomycin, CD: Clindamicin, TE: Tetracycline, AZ: Azithromycin, COT: Cotrimoxazole, GEN: Gentamicin, TOB: Tobramycin, NET: Netilmicin, A: Ampicillin, AZT: Aztreonam, ME: Meropenem, CAZ: Ceftazidime, AK: Amikacin, CEP; Cefipime, CTX: Cefotaxime, PIP-TAZ: Piperacillin-Tazobactam, AMC: Amoxicillin-Clavulanate

Table (5):
Prevalence rate of various etiological agents causing microbial keratitis in various studies.

In current study among the fungal isolates, Fusarium species was the predominant species isolated from cases of infective keratitis, followed by Aspergillus species. (Table 3) Similar results were reported in studies conducted by Ranjini et al.¹⁸ in South India and Jisha et al.²⁴ in Kerela. However, Alkantan et al.²⁵ from Saudi Arabia and Kartara et al.²⁶ from Gujarat, India, have reported Aspergillus species as the predominant fungus isolated from corneal ulcers in their respective studies. The difference in the predominant fungus isolates from the corneal ulcers could be due to differences in climatic and environmental variations from region to region. While spores of Aspergillus species are ubiquitously present in the environment, Fusarium species are common plant pathogens and can gain easy entry in case of traumatic injury by vegetative matter. Furthermore, it has been seen that keratitis caused due to Fusarium species has a more intrusive course and is comparatively less responsive to treatment than the keratitis caused by Aspergillus species.²⁷

In the present study, Gram positive bacteria were predominantly responsible for bacterial keratitis. The observation is comparable to other Indian studies by Gopinathan et al.²⁸ and Ranjini et al.²⁰ The predominant bacteria isolated in the present study was Staphylococcus aureus followed by Coagulase negative Staphylococcus species. Pseudomonas aeruginosa was the predominant Gram-negative bacteria isolated from the cases of bacterial keratitis, followed by Klebsiella species. (Table 3)

The observation of the present study is comparable to the study conducted in Pakistan by Narsani et al.²⁹ which reported Staphylococcus aureus was the predominantly isolated species from the cases of infective keratitis while in Hong Kong, Lam et al.³⁰ reported Pseudomonas species as predominant bacteria in their study.

The standard treatment of bacterial corneal ulcer varies depending upon the clinician’s presentation, duration and etiological agent the ophthalmologist is suspecting and the culture results. In most eye care clinics and tertiary care setups, topical antibiotics are prescribed. In the present study, both topical as well as systemic antibiotics were tested for bacteria.

The antibiotic sensitivity pattern in the present study showed that all Gram positive bacteria were 100 percent sensitive to vancomycin, azithromycin, linezolid and oxacillin. For the drugs given as topical antibiotics, the sensitivity of Staphylococcus aureus was 83.3 % (10/12) for levofloxacin and clindamycin both, followed by 66.6% (8/12) for cotrimoxazole, 58.3% (7/12) for tetracycline and least 50% (6/12) for tetracycline and gentamicin both. Coagulase negative Staphylococcus also showed 100 % (12/12) sensitivity for both levofloxacin and clindamycin and the least for gentamicin with 50% (4/8) (Table 4).

Among the Gram negative isolates, predominantly isolated bacteria, Pseudomonas aeruginosa showed 100 percent susceptibility to piperacillin/tazobactam, aztreonam, and meropenem, followed by 90% sensitivity to cefotaxime. For antimicrobials that are prescribed for topical use, maximum sensitivity was observed for levofloxacin 75 % (3/4) followed by tobramycin 50% (2/4), amikacin 50% (2/4) and ciprofloxacin 50% (2/4). The least sensitivity was seen for netilmicin 25 % (1/3) and gentamicin 25 % (1/3) (Table 4).

The overall sensitivity of bacterial isolates varies from region to region as reported by various studies.^10,18,20 The irrational use of topical antibiotics, non-compliance to the treatment and over the counter availability of these drugs in India could be the reason for developing resistance to topical antibiotics.

Limitation of this study was that it was a single tertiary center study. To get a broader picture of the etiological agents of this disease a multicentric study of the region is required. Since the maximum number of patients in the study belonged to rural areas, it is important to collaborate with rural health setups providing medical services to the population of the region.

Another limitation of the study was that, the study started during the initial waves of the COVID-19 pandemic in India, when there were restrictions and patients hesitated to come to the hospital for treatment. Due to this factor the number of subjects in the study was less than expected.

Another limitation of this study was that we did not include anaerobes, amoebic and viral agents causing keratitis, therefore only aerobic bacterial and fungal aspects of the disease were studied. All the aspects of infectious keratitis were not included as it was not feasible to perform advanced tests. Although not many studies have been conducted to study the anaerobes in cases of a corneal ulcers due to feasibility and financial issues but many years back in 1982, a study was conducted by Perry et al.³¹ that had reported a prevalence of 16.66% of anaerobes to isolate from cases of corneal ulcers. Further studies which include the isolation of all pathogens associated with infective keratitis would give a better picture of the disease in that region.