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 ~  Results
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ORIGINAL ARTICLE
Year : 2003  |  Volume : 21  |  Issue : 4  |  Page : 239-245
 

Epidemiology of bacterial keratitis in a referral centre in South India


Department of Microbiology, Aravind Eye Care System, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli - 627 001, Tamil Nadu, India

Correspondence Address:
Department of Microbiology, Aravind Eye Care System, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli - 627 001, Tamil Nadu, India

 ~ Abstract 

PURPOSE: To study the epidemiological characteristics of bacterial keratitis seen at a tertiary eye care referral centre in south India. METHODS: A retrospective review of medical records of all culture-positive bacterial keratitis which were seen over a 3 years period, from September 1999 through August 2002 was performed. After clinical evaluation corneal scrapings were collected and subjected to culture and microscopy using standard protocols in all patients. RESULTS: Out of 3183 corneal ulcers evaluated, 1043(32.77%) were found to be of bacterial aetiology. A total of 1109 bacterial pathogens were isolated from 1046 eyes with keratitis. The predominant bacterial species isolated was Streptococcus pneumoniae (37.5%). Males were 592(56.76%) and 451(43.24%) were females. There were 564(54.07%) rural residents and 479(45.93%) urban residents; this difference was statistically significant (p< 0.0001). Patients with age more than 50 years (60.2%) were affected significantly more than patients aged less than 50 years (30.8%). While 57.62% of patients were non-agricultural workers, 42.38% were farmers; this difference was statistically significant (p<0.0001). Co-existing ocular diseases predisposing to corneal ulceration were identified in 703(67.4%) patients, compared to other predisposing risk factors in 340(32.6%) patients. One hundred and seventy seven (16.97%) had corneal injury with soil and/or sand, compared to 115(11.03%) patients who had injury due to other materials and the difference was statistically significant. There was lower incidence of bacterial keratitis from June to September. CONCLUSIONS: The epidemiological characteristics of bacterial keratitis vary geographically. This study describing the features of bacterial keratitis would greatly help the practising ophthalmologist and other medical practitioners in the management of their patients.

How to cite this article:
Bharathi M J, Ramakrishnan R, Vasu S, Meenakshi R, Shivkumar C, Palaniappan R. Epidemiology of bacterial keratitis in a referral centre in South India. Indian J Med Microbiol 2003;21:239-45


How to cite this URL:
Bharathi M J, Ramakrishnan R, Vasu S, Meenakshi R, Shivkumar C, Palaniappan R. Epidemiology of bacterial keratitis in a referral centre in South India. Indian J Med Microbiol [serial online] 2003 [cited 2019 Oct 23];21:239-45. Available from: http://www.ijmm.org/text.asp?2003/21/4/239/8035


Microbial keratitis is a common, potentially sight-threatening ocular infection that may be caused by bacteria, fungi, viruses or parasites.[1] Bacterial keratitis rarely occurs in the normal eye because of the human cornea's natural resistance to infection. However, predisposing factors such as corneal injury, contact lens wear, ocular adnexal dysfunction (including tear deficiencies), corneal abnormalities and other exogenous factors, systemic diseases and immunosuppression may alter the defense mechanisms of the outer eye and permit bacteria to invade the cornea.[2],[3] Bacterial corneal ulceration is an ocular emergency due to the often rapid progression of this corneal infection with the threat of visual loss and potential corneal perforation.[4] The majority of bacteria cultured from infections of cornea are of the same species that normally are present in the conjunctival sac, on the lids or periocular skin, and in the adjacent nasal passages.[2]
Considering the importance of corneal ulceration as an important cause of visual loss, many studies have reported the prevalence of microbial pathogens and identified the risk factors predisposing a population to corneal infection in south India.[5],[6],[7] The aetiological and epidemiological patterns of corneal ulceration have been found to vary with the patient population, health of the cornea, geographic location and climate, and also tends to vary somewhat over time.[8] Hence, an understanding of the epidemiological features, risk factors and aetiological agents that occur in specific region are important in rapid recognition, timely institution of therapy, optimal management and prevention of this disease entity. In order to start specific therapy, it is necessary to do meticulous laboratory investigations, and this includes microscopy and culture of corneal scrapings.
The purpose of this study was to determine the risk factors and other epidemiological characteristics, and to identify specific bacterial pathogens causing bacterial keratitis in patients presenting at a tertiary referral eye care centre in south India.

 ~ Materials and Methods Top

Patients
A retrospective analysis of all patients with culture-proven bacterial keratitis seen over a period of three years from September 1999 to August 2002 was performed. A total of 3183 consecutive patients with corneal ulceration were analysed. Ulceration was defined as a loss of the corneal epithelium with underlying stromal infiltration and suppuration associated with signs of inflammation with or without hypopyon. Ulcers with typical features of viral infection and healing ulcers were excluded as were Mooren's ulcers, interstitial keratitis, sterile neurotropic ulcers, and any ulcer associated with autoimmune conditions. Data related to sociodemographic features, duration of symptoms, predisposing factors, history of corneal trauma, traumatic agents, associated ocular conditions, other systemic diseases, therapy received prior to presentation, visual acuity at the time of presentation and all clinical findings were collected from medical records of the patients.
All patients had undergone thorough slit-lamp biomicroscopic examination by an ophthalmologist. After a detailed ocular examination, using standard techniques, corneal scrapings were taken under aseptic conditions from each ulcer by an ophthalmologist using a sterile Bard-Parker blade (No 15).[6],[9],[10] The procedure was performed under the magnification of a slit-lamp or operating microscope after instillation of 4% lignocaine (lidocaine) without preservative. The material scraped from the leading edge and the base of each ulcer was initially directly inoculated onto the surface of solid media such as 7% sheep blood agar, chocolate agar and Sabouraud glucose neopeptone agar (pH 5.6 + 0.2, Carlier modification of Sabouraud formulation) in a row of C- shaped streaks. Material was also inoculated into the depth of liquid media such as brain heart infusion broth and thioglycollate medium. The material obtained by scraping was also spread onto labeled slides in a thin, even manner to prepare a 10% potassium hydroxide (KOH) wet mount and to prepare smear for Gram staining and Giemsa staining. In cases of suspected actinomycete keratitis, Kinyoun's method of acid fast staining was performed. When KOH smears revealed cysts with the morphology of Acanthamoeba spp. further corneal scrapings were performed and the material was inoculated onto non-nutrient agar. Meticulous care was taken in the collection of material and in transferring it aseptically to the appropriate culture media.
Laboratory Procedures
All inoculated media were incubated aerobically. The inoculated Sabouraud dextrose agar were incubated at 270C, examined daily, and discarded at three weeks if no growth was seen. The inoculated plates of blood agar and chocolate agar, and tubes of thioglycollate broth and brain heart infusion broth were incubated at 370C, examined daily, and discarded at 7 days if growth was not seen. Broth tubes were held upright in racks. The inoculated non-nutrient agar plates were incubated at 370C after overlaying with  Escherichia More Details coli broth culture and were examined daily for the presence of Acanthamoeba spp. and discarded at three weeks, if there were no signs of growth. All laboratory methods followed standard protocols.[6],[9],[10] Microbial cultures were considered significant if growth of the same organism was demonstrated on more than one solid phase medium, and/or if there was confluent growth at the site of inoculation on one solid medium, and/or if growth of one medium was consistent with direct microscopy findings (i.e., appropriate staining and morphology with Gram stain) and/or if the same organism was grown from repeated scraping. Pearson's chi-square test was used to carry out the statistical analysis wherever required.

 ~ Results Top

Microbiological profile
Bacteria alone were recovered in culture from the corneal scrapings of 1043(32.77%) patients, fungi alone from 1095(34.4%), Acanthamoeba alone from 33(1.04%) and both bacteria and fungi from 76(2.39%). There was no growth in culture from the corneal scrapings of 936(29.41%) patients. Of the 1043 culture positive bacterial keratitis cases, one eye was infected in 1040(99.71%) patients and both eyes were infected in 3(0.29%) patients. Of the 1046 culture positive eyes, 983(93.98%) eyes had a single species of bacterial growth and 63(6.02%) eyes had two species of bacterial growth. A total of 1109 bacterial pathogens were isolated from the 1046 eyes which yielded only bacterial growth in culture. Of the 1109, 722(65.1%) were gram positive cocci, 274(24.71%) were gram negative bacilli, 55(4.96%) were gram positive bacilli, 46(4.15%) were aerobic actinomycetes (Nocardia spp.) and 12(1.08%) were gram negative cocci and coccobacilli. The predominant bacterial species isolated were Streptococcus pneumoniae 416(37.5%) followed by Pseudomonas aeruginosa 200(18.03%) and Staphylococcus epidermidis 193(17.4%).
Demographics
Out of 1043 patients 592(56.76%) were males and 451 (43.24%) were females. There were 564 (54.07%) rural residents and 479 (45.93%) urban residents and the difference was statistically significant (p<0.0001). Patients above the age of 50 years (628, 60.2%) were significantly (P<0.0001) more than patients below 50 years (415, 39.8%). Non-agricultural workers were significantly (P<0.001) more in number than were farmers (442, 42.38%).
Co-existing ocular diseases predisposing to corneal ulceration were identified in 703 (67.4%) patients, compared to other predisposing risk factors in 340 (32.6%) patients (p< 0.0001). The co-existing ocular diseases are shown in [Table - 2]. A history of corneal injury was recorded in 292(28%) patients, of which 177 (16.97%) had corneal injury with soil and/or sand and 115 (11.03%) had injury due to other materials. The percentage of patients who reported a history of corneal injury with soil and/or sand was significantly higher than the percentage reporting injury due to other traumatising agents (p<0.0001).
Of 1046 patients 550(52.58%) patients had bacterial corneal ulcers in the left eye, 493(47.13%) in the right eye and 3(0.29%) in both eyes. Figure depicts the seasonal distribution of 1043 culture positive bacterial keratitis cases analyzed over a period of three years. Our data revealed that in south India, there was lower incidence of bacterial keratitis from June to September than other months.

 ~ Discussion Top

At birth the eyes are sterile but they soon become invaded by various bacteria and other microorganisms. The conjunctival sac and lid margins of the eye harbour a variety of bacteria. The interior structures are sterile.[11] The bacteria that are normally present can be arranged in two groups; the resident bacteria which are constantly present in the eye and which if disturbed, promptly re-establish themselves (Corynebacterium spp.); the transient bacteria which consist of non-pathogenic or potentially pathogenic bacteria that inhabit the eye for short periods.[11] Almost any species of bacteria can infect the cornea if the integrity of the natural anatomic barriers or defense mechanisms is compromised.[11],[8] The present study describes features of 1043 culture-proven cases of bacterial keratitis diagnosed at a tertiary eye care centre in south India over a period of three years.
In this study, bacterial keratitis accounted for 32.77% out of 3183 corneal ulcers evaluated. Bacterial keratitis has been reported to account for 32.3% of all cases of corneal ulcer evaluated in Madurai (south India),[6] 29.3% in Thiruchirapalli (south India),[5] 35.6% in south Florida[12] and 25% in southern Ghana.[13] In marked contrast, a study performed in Nepal documented the occurrence of a bacterial aetiology in 63.2% of all corneal ulcers.[14] Bacteria are responsible for a larger proportion of corneal ulceration in temperate climates such as Britain[15] and northern United States[16] than in tropical regions such a south India, but in the sub-tropical urban climates of Hong Kong bacteria are a predominant cause for microbial keratitis.[17]
Of 1043 patients, 1040(99.71%) had unilateral bacterial keratitis and 3(0.29%) bilateral bacterial keratitis and there was a total of 1109 bacterial isolates. Of the 1046 eyes, 983(93.98%) had single species of bacterial growth and 63(6.02%) had two species of bacterial growth. Streptococcus pneumoniae (37.51%) was the predominant bacterial species in this study and was similar to the reports from Madurai,[6] Trichirapalli[5] and Nepal.[14] In contrast, predominance of Pseudomonas aeruginosa in Ghana[13] and Hong Kong,[17] and Staphylococcus spp in south Florida,[12] Switzerland[18] and Hyderabad[19] have been reported. These reports show that there is distinct pattern of geographical variation in the aetiology.
Male preponderance (56.76%) was noted in our study, but it is not statistically significant (p= 0.075)). The incidence of bacterial keratitis was 45.93% in urban and 54.07% in rural area and this difference was statistically significant. Urban residents have 2.98(95% Confidence Interval: 2.54 - 3.4) times higher odds of getting bacterial keratitis. In marked contrast, significantly higher incidence of Nocardia keratitis has been reported among rural residents and accounted for 24(77.24%) of 31 culture-positive Nocardia keratitis evaluated in our previous study.[20]
There was significantly higher incidence of bacterial keratitis among patients other than agricultural workers (p<0.0001). This study shows that there is significant association between occupation and bacterial keratitis. Those who are occupied elsewhere are 2.88(95% CI: 2.47 - 3.36) times more prone to bacterial keratitis than those who are engaged in farm work, while the higher incidence of Nocardia spp. keratitis has been reported among farmers (71%) in our previous study.[20]
Bacterial keratitis is significantly higher (60.21%) among those aged >50 years in our present study (p<0.0001). Those aged >50 years are 6.11(95% CI: 5.19% - 7.19%) times more prone to bacterial keratitis than those less than 50 years. This is in contrast to fungal keratitis which affects more of younger age group (21-50 years).[6]
Corneal trauma is the leading cause of microbial keratitis.[6],[14],[21] However, in the present study the most common risk factors identified for the development of bacterial keratitis was co-existing ocular diseases. There is significant (p<0.0001) association between associated ocular conditions and bacterial keratitis. Eyes that have co-existing ocular diseases are 33.99(95% CI+: 27.37 - 42.21) times more prone to bacterial keratitis than those that do not have any. Similarly Schaefer et al reported that co-existing ocular diseases and contact lens wear were predominant predisposing factor (80%) for the development of bacterial keratitis.[18] In marked contrast, corneal injury has been reported as the predominant predisposing factor for the development of Nocardia keratitis in our previous study[20] and Gopinathan et al reported higher incidence of fungal keratitis due to corneal injuries in Hyderabad.[22] Chronic dacryocystitis and spheroidal degeneration were the most common risk factors and they were encountered in 242(23.2%) and 234(22.44%) patients respectively in our study. Severe blepharitis was present in 74(7.09%) patients. Loose suture infiltrates extending to corneal ulceration was noted in 30(2.88%) patients. 26(2.49%) patients had conjunctivitis, 24(2.3%) had dry eye syndrome and other complications such as bullous keratopathy, pre-existing viral keratitis, lid abnormalities, Bell's palsy, lagophthalmos, trichiasis and adherent leucoma were seen to be co-existing in 73(7%) patients.
A history of corneal trauma associated with bacterial keratitis was documented in 292(28%) patients. Corneal injury with soil, sand and / or stone resulting in bacterial keratitis was significantly more than with any other material (p<0.0001). Those eyes that had an injury where soil was the agent had 5.89(95% CI: 4.54% - 7.62%) times the odds of bacterial keratitis than those that had trauma by other agents. Gopinathan et al found vegetative matter as the principal traumatic agent for the development of fungal keratitis.[22] Bacterial keratitis associated with contact lens wear was documented in 33(3.16%) patients and all 33(100%) had gram negative bacilli growth. Similarly Houang et al reported the predominance of gram-negative bacilli from corneal ulcers of contact lens wearers.[17] Prolonged use of topical steroids resulting in bacterial keratitis was identified in 7(0.67%) patients and all of the 7 cases had Streptococcus pneumoniae. Houang et al isolated gram-positive cocci, gram-negative bacilli and fungus from patients using topical steroids. In addition, 8(0.77%) patients had systemic disease, of which 6(0.58%) had leprosy and 2(0.19%) had  Stevens-Johnson syndrome More Details.
In this study, the incidence of bacterial keratitis was less when compared with fungal keratitis during the months of June to September. In comparison, the incidence of fungal keratitis was higher during the month of June, July, August and September because of paddy harvesting and other agricultural activities. The peak incidence of fungal keratitis also correlates with windy and dry weather during June thorough September.
In summary, bacterial keratitis is rare in the absence of predisposing factors and it is frequently encountered in patients with co-existing ocular disease and contact lens wear. The epidemiology and aetiology of bacterial keratitis is specific to the region. Screening patients for predisposing factors, treating the co-existing ocular diseases and educating them about proper lens care and the risk of infection, may reduce the occurrence of bacterial keratitis. It is necessary to be aware of its risk factors, have a suspicion of its presence, have a good microbiology workup for establishing timely institution of therapy in order to preserve vision. 

 ~ References Top

1.O'Brien TP. Bacterial keratitis, Chapter 94. In: Cornea: Cornea and External Diseases, Clinical Diagnosis and Management. Krachmer JH, Mannis MJ, Holland EJ, Eds. (St. Louis, Mosby). 1997:1139-1189.   Back to cited text no. 1    
2.Reddy M, Sharma S, Rao GN. Corneal Ulcer. In: Modern Ophthalmology. 2 nd ed. Dutta LC. Eds (Jaypee Brothers Medical Publishers, New Delhi) 2000;1:200-216.  Back to cited text no. 2    
3.Abbott RL, Kremer PA, Abrams MA. Bacterial Corneal Ulcers. Chapter 18 In: Duane's Clinical Ophthalmology. Tasman N, Jaeger EA, Eds. (J.B Lippincott Company, Philadelphia) 1994;4:1-36.  Back to cited text no. 3    
4.Ogawa GS, Hyndiuk RA. Bacterial Keratitis and Conjunctivitis - Clinical Disease. In: The Cornea: Scientific Foundations and Clinical Practice. 3rd ed. Smolin G, Thoft RA, Eds. (Little, Brown and Company, Boston) 1994:125-167.  Back to cited text no. 4    
5.Leck AK, Thomas PA, Hagan M, Kaliamurthy, Ackuaku E, John M, et al. Aetiology of suppurative corneal ulcers in Ghana and south India, and epidemiology of fungal keratitis. Br J Ophthalmol 2002;86:1211-1215.  Back to cited text no. 5    
6.Srinivasan M, Gonzales CA, George C, Cevallus V, Mascarenhas JM, Asokan B, et al. Epidemiology and aetiological diagnosis of corneal ulceration in Madurai, south India. Br J Ophthalmol 1997;81:965-971.  Back to cited text no. 6    
7.Bharathi MJ, Ramakrishnan R, Vasu S, Meenakshi R, Palaniappan R. Aetiological diagnosis of microbial keratitis in south India. Indian J Med Microbiol 2002;20:19-24.  Back to cited text no. 7    
8.Burd EM. Bacterial Keratitis and Conjunctivitis - Bacteriology. In: Smolin G, Thoft RA, Eds. The Cornea: Scientific Foundations and Clinical Practices, 3rd ed. (Little, Brown and Company, Boston) 1994:115-124.  Back to cited text no. 8    
9.Jones DB, Liesegang TJ, Robinson NM. Laboratory diagnosis of ocular infections. (American Society for Microbiology, Washington DC) 1981.  Back to cited text no. 9    
10.Sharma S, Athmanathan S. Diagnostic procedures in infectious keratitis. In: Nema HV, Nema N, editors. Diagnostic procedures in ophthalmology. (Jaypee Brothers Medical Publishers, New Delhi) 2002:232-253.  Back to cited text no. 10    
11.Sharma S. Ocular Microbiology. 1st ed. (Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Madurai) 1988.  Back to cited text no. 11    
12.Liesegang TJ, Forster RK. Spectrum of microbial keratitis in south Florida. Am J Ophthalmol 1980;90:38-47.  Back to cited text no. 12    
13.Hagan M, Wright E, Newman M, Dolin P, Johnson GJ. Causes of suppurative keratitis in Ghana. Br J Ophthalmol 1995;79:1024-1028.  Back to cited text no. 13    
14.Upadhyay MP, Karmacharya PC, Koirala S, Tuladhar N, Bryan LE, Smolin G, et al. Epidemiologic characteristics, predisposing factors, and etiologic diagnosis of corneal ulceration in Nepal. Am J Ophthalmol 1991;111:92-99.  Back to cited text no. 14    
15.Coster DJ, Wilhelmus K, Peacock J, Jones BR. Suppurative keratitis in London. IVth Congress of the European Society of Ophthalmology. Royal Society of Medicine International Congress and Symposium Series No 40. London, 1981:395-398.   Back to cited text no. 15    
16.Asbell P, Stenson S. Ulcerative keratitis. Survey of 30 years laboratory experience. Arch Ophthalmol 1982;100:77-80.  Back to cited text no. 16    
17.Houang E, Larn D, Fan D, Seal D. Microbial keratitis in Hong Kong: relationship to climate, environment and contact-lens disinfection. Trans Roy Soc Trop Med Hyg 2001;95:361-367.  Back to cited text no. 17    
18.Schaefer F, Bruttin O, Zografos L, Guex-Crosier Y. Bacterial keratitis: a prospective clinical and microbiological study. Br J Ophthalmol 2001;85:842-847.  Back to cited text no. 18    
19.Sharma S, Kunimoto DY, Garg P, Rao GN. Trends in antibiotic resistance of corneal pathogens: Part I. An analysis of commonly used ocular antibiotics. Indian J Ophthalmol 1999;47:95-100.   Back to cited text no. 19    
20.Bharathi MJ, Ramakrishnan R, Vasu S, Meenakshi R, Chirayathi A, Palaniappan R. Nocardia asteroides keratitis in South India. Indian J Med Microbiol 2003;21:31-36.  Back to cited text no. 20    
21.Thylefors B. Epidemiological pattern of ocular trauma. Aust NZ J Ophthalmol 1992;20:95-98.  Back to cited text no. 21    
22.Gopinathan U, Garg P, Fernandes M, Sharma S, Athmanathan S, Roa GN. The epidemiological features and laboratory results of fungal keratitis: a 10-year review at a referral eye care center in south India. Cornea 2002;21:555-559.  Back to cited text no. 22    
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