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Original Article

Epidemiological and Microbiological Diagnosis of Suppurative Keratitis in Gangetic West Bengal, Eastern India

Basak, Samar K MD, DNB; Basak, Sukumar MD; Mohanta, Ayan MS; Bhowmick, Arup MS

Author Information
Indian Journal of Ophthalmology: Jan–Mar 2005 - Volume 53 - Issue 1 - p 17-22
doi: 10.4103/0301-4738.15280
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Abstract

Corneal infections are the second most common cause of monocular blindness after unoperated cataract in some developing countries in the tropics.123 The incidence of microbial keratitis varies from 11 per 100,000 persons/year in the United States to 799 per 100,000 persons/year in Nepal.45 The associated ocular morbidity is the result of several factors and patients′ management is directly affected by the lack of diagnostic facilities and initiation of appropriate antimicrobial therapy. Specific treatment requires quick and accurate identification of the causative micro-organisms.6

The epidemiological pattern and causative agents for suppurative corneal ulcer varies significantly from country to country, and even from region to region within the same country. It is important to determine the “regional” aetiology within a given region for comprehensive strategy for the diagnosis and treatment of corneal ulcer.6 Several studies have addressed these questions in the Indian subcontinent.1257891011121314151617181920 But only one small-size study is available from rural Bengal19 and one study on fungal keratitis from Assam (Medline Search).20 A comprehensive data as regards to the demographical and aetiological factors of suppurative corneal ulcerations from eastern India is not available.

The purpose of this study was to evaluate all suppurative keratitis seen at a semi-urban large eye hospital in West Bengal, eastern India, over a period of three years from January, 2001 to December, 2003. We also attempted to search for the antecedent risk factors predisposing to the development of suppurative keratitis and to identify the specific microorganisms responsible for infections. We believe this will help in management of such cases in this region.

Materials and Methods

Patients

The data on suppurative keratitis was collected prospectively at Disha Eye Hospitals and Research Centre, Barrackpore, West Bengal in between 1 January, 2001 to 31 December, 2003. Disha Eye Hospitals and Research centre is a tertiary care eye institute in eastern India that caters to the patients from North 24-Parganas district and surrounding four Districts of Gangetic West Bengal, a population of over 10 million.

All patients were included consecutively after the initial clinical diagnosis of suppurative corneal ulcer was made. Corneal ulcer was defined as a loss of the corneal epithelium with underlying stromal infiltration and suppuration associated with signs of inflammation with or without hypopyon.7 The ulcers excluded from this study were: typical or suspected viral ulcers, healing ulcers, Mooren′s ulcer, marginal keratitis, interstitial keratitis, atheromatous ulcer, neurotrophic keratitis, and any ulcer associated with systemic or autoimmune diseases. A standardised form was completed for each patient documenting socio-demographic information as well as clinical findings including duration of symptoms, past treatment, time of presentation, predisposing ocular conditions and associated systemic risk factors amongst other clinical details.

Clinical procedure

The visual acuity was measured in a standard manner. All patients were examined under slitlamp biomicroscope by an ophthalmologist. The size of the ulcer was measured after staining with wet sterile fluorescein paper strip using the variable slit on the slit lamp and recorded in millimeters. In a similar way, size of the stromal infiltrate and depth of the lesion was recorded. Ulcer margin, floor, thinning, satellite lesions, pigmentation on the ulcer surface, any impacted foreign body were noted. The presence of hypopyon was recorded and its height was measured in millimeters. Any associated ocular condition like trichiasis/entropion, blepharitis, Bell′s palsy, lagophthalmos, chronic dacryocystitis, dry eyes, corneal anaesthesia, bullous keratopathy, spheroidal degeneration of the cornea, any surgery on the cornea, use of contact lens, or ocular leprosy was also noted. The use of topical medications including topical corticosteroids were also noted.7,18

Corneal scraping was performed under strict aseptic conditions by an ophthalmologist using a sterile Bard-Parkar blade (No 15).18,21 The procedure was performed under magnification of a slitlamp or binocular loupe following instillation of preservative-free 2% lignocaine hydrochloride. Material obtained from scraping of the leading edge and base of each ulcer was inoculated in the media and smeared onto two slides, one stained with Gram stain and the other with 10% Potassium hydroxide (KOH) for direct microscopic evaluation.6

Laboratory procedures

For bacterial cultures, the materials were inoculated aerobically at 370 C onto blood agar, chocolate agar, and potato dextrose agar (PDA). Cultures on blood agar and chocolate agar was evaluated at 24 hours and 48 hours, and then discarded if there was no growth. For fungal cultures the materials were inoculated on to Sabouraud dextrose agar (SDA) and incubated at room temperature, examined daily, and discarded after 2 weeks if there was no growth. When KOH smears were positive for amoebic cysts, a further corneal scraping was performed and the material was inoculated onto non-nutrient agar overlaid with Escherichia coli; this was discarded if there was no growth after 7 days.6 Bacterial cultures were considered positive only if growth of the same organism was demonstrated on both media or there was semi confluent growth at the site of inoculation on one media with identification of morphological characteristics of similar organism in Gram Stain.6

The specific identification of bacterial pathogens was based on microscopic morphology, staining characteristics and biochemical properties using standard laboratory criteria. Fungi were identified by their colony characteristics on SDA and by the morphological appearance of the spores in lactophenol cotton blue stain, and in some cases by slide culture method. If by microscopy in KOH mount preparation, hyphae were observed in corneal smear, but failed to grow in culture, the causative organism was reported as fungal.6 All laboratory methods followed standard protocols which have been discussed in details in previous publications.1,6718

Results

Epidemiological Characteristics

1198 patients with the clinical diagnosis of corneal ulcer with or without hypopyon were enrolled for this study. 846 (70.6%) patients were males and 352 (29.4%) were females (p< 0.0001). In both groups, keralitis occurred most frequently (591; 49.3%) in the age group 21-40 years (P< 0.0001). Most of the patients (941; 78.5%) were from rural areas (P< 0.0001). The majority (691; 57.6%) were farmers or agricultural workers, usually working in paddy or jute fields. A majority of the patients (621; 51.8%) were seen between 2-3 weeks of their illness at our hospital and 156 (13%) patients reported after 4 weeks. There was a significant increase in patients (297; 24.8%) during the month of November and December (Table 1). Primary care was sought by 1056 (88.1%) patients before their first visit to us. Among them, 538 (50.9%) patients were seen by ophthalmologists, (142; 13.4%) received advice from ophthalmic assistants, (106; 10.0%) went to general physician, (224; 21.2%) received advice from chemists and 29 (2.3%) patients went to physicians of alternative medicine (Homeopathy, Ayurved). Only 7 (0.67%) patients went to village healers. 393 (37.22%) patients consulted two or more physicians before presenting to us.

Table 1
Table 1:
Demographic characteristics of suppurative corneal ulcers seen at a tertiary eye-care-centre in eastern India

Of the patients who were on some form of topical medication (n = 1056), 918 (86.9%) were taking antibiotic drops (ciprofloxacin, tobramycin, ofloxacin, chloramphenicol, or sparfloxacin), 194 (18.4%) patients were taking antifungal eye drops, (natamycin or itraconazole), 136 (12.8%) were on acyclovir eye ointment, 231 (21.8%) were taking topical corticosteroids and in 34 (3.2%) patients the name of medication could not be ascertained.

Predisposing factors

A history of recent corneal injury was obtained in 994 (82.9%) patients. 715 (59.6%) patients had corneal injury with vegetative matter; mostly (526; 43.9%) paddy or paddy stalk (P< 0.0001), followed by jute plant (128; 10.6%). Other significant agents were twig of a tree, flying insect, dirt, mud, sand, etc. Ocular problems predisposing to corneal ulcer were present in 121 (10.1%) patients. Among them, 29 (2.4%) patients had chronic dacryocystitits and 18 (1.5%) had dry eyes. In addition, 8 patients were postsurgical and 4 patients were soft contact lens users. 92 (7.6%) were diabetic and 6 patients had leprosy (Table 2). The risks for suppurative keratitis associated with these predisposing conditions were presumptive.7

Table 2
Table 2:
Predisposing factors of suppurative corneal ulcers seen at a tertiary eye-care centre in eastern India

Microbial Diagnosis

Cultures were positive in 811 (67.7%) corneal ulcers. 509 (42.5%) patients had pure fungal growth, 184 (15.3%) had pure bacterial growth, 114 (9.5%) cases had mixed bacterial and fungal growth, and 4 (0.3%) patients were positive for Acanthemoeba. The remaining 387 (32.3%) patients were culture negative (Table 3). 298 bacterial growths were obtained from 184 patients. Of the 298 isolates 214 (71.8%) were gram positive and 84 (28.2%) were gram negative. Staphylococcus aureus was the most commonly isolated bacterial organism (127; 42.6%) of all positive bacterial cultures. The other isolated gram-positive organisms were Staphylococcus epidermidis (15.7%), Streptococci pneumoniae (9.4%), and Diphtheroids. Pseudomonas spp, the most frequently occurring gram-negative organism was isolated from 63 (21.1%) cultures (Table 4). The other gram-negative organisms were Enterobactor spp, Moraxella spp, Haemophilus influenzae, etc. There were 623 fungal isolates in 509 patients - 373 (59.8%) grew Aspergillus spp, 132 (21.2%) grew Fusarium spp and 63 (10.1%) grew Penicillium spp. Yeast form, Candida spp was positive in 7 (1.1%) cases. Dematiacious fungi, such as Curvularia, Alternaria, Bipolaris and Cladosporium were present in 12 (1.7%) cases (Table 5).

Table 3
Table 3:
Causative micro-organisms responsible for corneal ulcers in eastern India.
Table 4
Table 4:
Identification of the bacterial isolates from corneal ulcers in eastern India
Table 5
Table 5:
Identification of the fungal isolates from corneal ulcers in eastern India

Discussion

In this study, the majority of the corneal ulcer patients (70.7%) were agricultural workers and daily wage earners, an occupation profile similar to south Indian study7,18 (66.8% and 79.3% respectively), but in contrast to Ghana, where only 16.1% of the patients were agricultural workers.22 Undoubtedly, ocular injury with paddy or its stalk was the most common (43.91%) predisposing factor in this study, followed by jute plant (10.7%), another important crop in Gangetic West Bengal. Any preventive programme obviously should address this occupation related corneal trauma.

Unlike south India (60%),7 only 132 (11.1%) patients in this study presented during the first week of their illness. Before their first presentation at our hospital, 1056 (88.1%) patients had consulted health-care provider of some kind, and 680 (56.7%) of them had consulted ophthalmic personnel. Similar to the south India, most eye medications are sold over the counter without a prescription in West Bengal and it is not a surprising observation that 224 (18.7%) patients received some form of topical medication from a chemist before their first consultation. It is also a matter of serious concern that 231 (19.3%) patients were on topical corticosteroids for variable duration. This was in contrast to the reports of 8% and 1.1% from south India.718

A significant increase (297; 24.8%) in the number of cases of suppurative keratitis was observed during harvesting seasons of November-December (p< 0.001). Others have noted an increase incidence of fungal keratitis during the dry, windy, harvesting seasons compared with the wet, humid months of the year,691023 and few others have reported an increase during the hot and humid months.152224

In this study 811 (67.7%) of 1198 corneal scrapings were culture positive. This is similar to reports in Ghana6 and south India,718 57.3%, 68.4% and 70.6% culture positive respectively. Culture and/or smear- positive fungi were identified as the principal aetiologic agent in 596 (49.7%) patients of all corneal ulcers. Among these, 87 (7.2%) cases were only smear-positive for fungus. 114 (9.5%) patients with mixed infections were considered primarily fungal for therapeutic reasons. So a total of 710 (59.3%) were treated as fungal infection. This figure is higher than the south Indian reports by Srinivasan et al,7 (51.9%) Leck et al,6 (44.1%) Bharathi et al.18 It is also higher than the study from Assam, eastern India where the incidence of fungal keratitis was 32%. Mixed infections both by bacteria and fungi were also more (9.5%) in the current series as compared to the reports by Srinivasan et al (5.1%),7 Leck et al (5.5%)6 and Bharathi et al (2.4%)18 from south India.

298 (24.8%) were bacteria positive, 15.3% had pure bacterial infection and 9.5% had a mixed infection. This reduction in bacterial corneal ulcers in general at the referral centres might be attributed to more successful treatment of bacterial corneal ulcers in the periphery since the introduction of topical fluoroquinolones in the late 1990s.24 Of the 298 bacterial isolates, 42.6% was Staphylococcus aureus, which was similar to the early study from Bengal.20 The most common infecting bacteria was Streptococcus pneumoniae in Nepal and south India,157 and Pseudomonas spp in Ghana and Bangladesh.69

The most commonly isolated fungal pathogens in the current series were Aspergillus spp. Of 623 fungal isolates, 59.8% were Aspergillus spp, 21.2% were Fusarium spp and 10.1% were Penicillium spp. In our study, Candida spp [(7; 1.12%) and pigment-producing dematiaceous fungi (12; 1.78%)] were less compared to other studies.118Aspergillus species were predominate in Mumbai, parts of south India, north India, Nepal and Bangladesh.191213161718 Other studies in south India have reported Fusarium spp to be more common than Aspergillus spp.6821Fusarium spp have also been found to be the principal fungal pathogen in Florida, Paraguay, Nigeria, Tanzania, Hong Kong and Singapore.42526272829303132 This phenomenon may be explained by differences in climate and the natural environment. Acanthamoeba infections were present in 4 (0.3%) patients. Two of them were contact lens wearers, and the other two patients gave a history of trauma to the eye while takeing bath on pond.

In summary, suppurative keratitis continues to be a cause for concern among the ophthalmologists in West Bengal and it is evident that predominance of agricultural activity in the Gangetic West Bengal is the principle causative factor. This “regional” information is important with regard to empirical management, as many eye clinics in the locality do not have microbiology facilities. It will also help us formulate guidelines for prevention of suppurative keratitis in the population at risk.

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Keywords:

Suppurative keratitis; epidemiology; Gangetic West Bengal

© 2005 Indian Journal of Ophthalmology | Published by Wolters Kluwer – Medknow