several risk factors such as contact lens wear , trauma , ocular surface disease , ocular surgery , and systemic disease have been reported to predispose patients to corneal infections .
management of microbial keratitis commonly involves obtaining corneal scrapings for microbiological studies , and then , empiric broad - spectrum treatment is typically initiated before culture results are available .
appropriate empiric therapy is selected by practitioners on the basis of epidemiological information such as predisposing factors and the spectrum of causative organisms .
for example , trauma is a common risk factor for fungal keratitis in developing agricultural countries , whereas contact lens wear is the main risk factor for bacterial keratitis in developed countries .
thus , it is essential to establish related information on microbial keratitis , including patient - specific risk factors and the most likely causative organisms , which would facilitate the development of effective strategies for the prevention , diagnosis , and treatment of microbial keratitis . in taiwan
, a study from a university hospital reported that contact lens - related pseudomonas keratitis was the most common form of microbial keratitis from 1992 to 2001 .
conducting periodic surveys of infectious keratitis is crucial for updating the local information for reference by clinicians because epidemiologic patterns may change over time .
therefore , the present study collected data on the predisposing factors , clinical manifestations , spectrum of microorganisms , and treatments for patients with microbial keratitis who were admitted to and treated at chang gung memorial hospital ( cgmh ) , a major teaching hospital in northern taiwan , from 2003 to 2012 .
this study was conducted as a retrospective , cross sectional design , and in accordance with the declaration of helsinki and was approved by the institutional research ethics board of cgmh , taiwan ( irb102 - 4073b ) .
consent was waived because of the retrospective design of the project and the anonymous analysis of the data .
we retrospectively reviewed the medical records of 558 patients with infectious keratitis who were admitted to cgmh from january 1 , 2003 to december 31 , 2012 .
we included patients with negative culture results if they presented with an epithelial defect and stromal infiltrate and responded favorably to antimicrobial treatment .
admission criteria were primarily severe ( ie , potentially sight - threatening ) keratitis and the need for intensive topical antimicrobials .
information on age , sex , predisposing factors , clinical features , microbiological results , treatments , and visual acuity ( if recorded ) was collected .
we defined an ulcer as being central if it encroached within 2  mm of fixation , peripheral if it involved a zone within 2  mm from the limbus , and paracentral if it was between the central and peripheral zone .
corneal ulcers were defined as being small ( < 2  mm ) , medium ( 26  mm ) , or large ( > 6  mm ) . corneal scrapings were obtained using a surgical blade and directly inoculated into blood agar , chocolate agar , modified sabouraud agar , lowenstein 
corneal scrapings of patients with clinical characteristics suggestive of acanthamoeba keratitis were inoculated into nonnutrient agar seeded with escherichia coli .
the various media were routinely incubated for a week or longer depending on the media before the final culture result was obtained .
a positive culture was defined as growth of at least 3 colonies along the line of inoculation on one solid medium on the basis of the criteria in a previous study . before the result of corneal ulcer culture
could be obtained , levofloxacin ( 0.5% ) alone or a combination of 2 fortified antibiotics ( 25  mg / ml of cefazolin and 25  mg / ml of amikacin ) was administered topically once per hour .
topical natamycin and amphotericin b ( 0.1% ) were applied hourly for mold and yeast infection , respectively .
topical polyhexamethylene biguanide ( 0.02% ) was applied for acanthamoeba keratitis . for data presentation , we arbitrarily divided the study years into 2 periods ; the first half was from 2003 to 2007 , and the second half was from 2008 to 2012 .
mantel - haenszel linear - by - linear association  test was used to detect the trends over the 10-year period .
categorical variables were analyzed using a  test ; continuous variables were analyzed using analysis of variance ( anova ) .
simple linear regression for univariate analysis was used to identify the factors associated with hospital stay .
all statistical analyses were performed using spss software , version 22 ( ibm , armonk , ny ) .
this study was conducted as a retrospective , cross sectional design , and in accordance with the declaration of helsinki and was approved by the institutional research ethics board of cgmh , taiwan ( irb102 - 4073b ) .
consent was waived because of the retrospective design of the project and the anonymous analysis of the data .
we retrospectively reviewed the medical records of 558 patients with infectious keratitis who were admitted to cgmh from january 1 , 2003 to december 31 , 2012 .
we included patients with negative culture results if they presented with an epithelial defect and stromal infiltrate and responded favorably to antimicrobial treatment .
admission criteria were primarily severe ( ie , potentially sight - threatening ) keratitis and the need for intensive topical antimicrobials .
information on age , sex , predisposing factors , clinical features , microbiological results , treatments , and visual acuity ( if recorded ) was collected .
we defined an ulcer as being central if it encroached within 2  mm of fixation , peripheral if it involved a zone within 2  mm from the limbus , and paracentral if it was between the central and peripheral zone .
corneal ulcers were defined as being small ( < 2  mm ) , medium ( 26  mm ) , or large ( > 6  mm ) .
corneal scrapings were obtained using a surgical blade and directly inoculated into blood agar , chocolate agar , modified sabouraud agar , lowenstein 
corneal scrapings of patients with clinical characteristics suggestive of acanthamoeba keratitis were inoculated into nonnutrient agar seeded with escherichia coli .
the various media were routinely incubated for a week or longer depending on the media before the final culture result was obtained .
a positive culture was defined as growth of at least 3 colonies along the line of inoculation on one solid medium on the basis of the criteria in a previous study . before the result of corneal ulcer culture
could be obtained , levofloxacin ( 0.5% ) alone or a combination of 2 fortified antibiotics ( 25  mg / ml of cefazolin and 25  mg / ml of amikacin ) was administered topically once per hour .
topical natamycin and amphotericin b ( 0.1% ) were applied hourly for mold and yeast infection , respectively .
, we arbitrarily divided the study years into 2 periods ; the first half was from 2003 to 2007 , and the second half was from 2008 to 2012 .
mantel - haenszel linear - by - linear association  test was used to detect the trends over the 10-year period .
categorical variables were analyzed using a  test ; continuous variables were analyzed using analysis of variance ( anova ) .
simple linear regression for univariate analysis was used to identify the factors associated with hospital stay .
all statistical analyses were performed using spss software , version 22 ( ibm , armonk , ny ) .
during the 10-year study period , 558 patients were included in this study , of which 285 ( 51.1% ) and 273 ( 48.9% ) were male and female , respectively ( table 1 ) .
the mean age of patients was 50.3    22.7 years ( range , 2100 yr ) .
the right eye was involved in 287 patients and the left eye was involved in 271 patients .
the corneal ulcer was small in 192 eyes ( 37.7% ) , medium in 267 eyes ( 52.5% ) , and large in 50 eyes ( 9.8% ) .
the location of the corneal ulcer was central in 238 eyes ( 47.1% ) , paracentral in 206 eyes ( 40.8% ) , and peripheral in 61 eyes ( 12.1% ) .
the presence of hypopyon was noted in 153 eyes ( 33.8% ) . except for laterality , trends for demographics and clinical features were not statistically significant . demographics and clinical features of microbial keratitis risk factors for microbial keratitis were identified in 426 patients ( 76.3% ) .
the most common risk factor was contact lens wear ( 31.4% ) , followed by systemic and ocular diseases ( 26.3% ) , trauma ( 23.5% ) , and previous ocular surgery ( 12.7% ) ( table 2 ) .
a total of 54 patients ( 12.7% ) had at least 2 predisposing factors for corneal ulcers .
materials causing ocular trauma included plant ( n  =  24 ) , iron ( n  =  16 ) , mud ( n  =  5 ) , chemical ( n  =  4 ) , wood ( n  =  3 ) , and unidentified sources ( n  =  48 ) .
lagophthalmos ( n  =  16 ) and dry eye ( n  =  14 ) were the most common ocular surface diseases .
the trend test showed that during the 10-year study period , the proportion of patients wearing contact lenses and with trauma increased ( p  =  0.011 and p  =  0.035 , respectively ) , and the rate of previous ocular surgery decreased ( p  =  0.027 ) .
predisposing factors for microbial keratitis positive culture results were obtained in 353 patients ( 63.3% ) .
two hundred thirty - eight ( 42.7% ) patients were administered topical antibiotics before referral , and 88 patients had negative culture results . regarding isolates , 210 bacterial isolates ( 59.9% ) , 62 fungal isolates ( 17.6% ) , 8 nontuberculous mycobacteria ( ntm ) isolates ( 2.3% ) , and 2 acanthamoeba isolates ( 0.6% ) were identified ( table 3 ) .
seventy - one patients had polymicrobial infections ( 20.1% ) . among bacterial isolates , gram - negative bacteria ( 37.4% ) were more common than gram - positive bacteria ( 22.1% ) .
the most commonly isolated bacterium was pseudomonas aeruginosa ( 28% ) , followed by coagulase - negative staphylococcus ( cns , 5.4% ) and staphylococcus aureus ( 4.5% ) .
the percentage of serratia marcescens decreased significantly ( p  =  0.033 ) ; the identified organisms did not change over 10 years .
isolated organisms in microbial keratitis table 4 lists isolated organisms from patients with different risk factors for microbial keratitis .
gram - negative bacteria , particularly p. aeruginosa , mainly accounted for contact lens - related keratitis ( 52.9% ) .
keratitis associated with ocular and systemic diseases was mainly caused by bacteria ( 33.8% and 29.4% for gram - positive and gram - negative bacteria , respectively ) .
risk factors versus isolated organisms in microbial keratitis all patients were initially treated with empiric antimicrobials , which were adjusted on the basis of the clinical response and the results of the drug susceptibility test .
medical treatment was successful for patients with gram - positive bacterial infections ( 62.8% ) , gram - negative bacterial infections ( 78% ) , ntm infections ( 75% ) , acanthamoeba infections ( 100% ) , and polymicrobial infections ( 74.6% ) ( table 5 ) .
surgical procedures included amniotic membrane transplantation , patch graft , lamellar keratectomy , penetrating keratoplasty , and evisceration .
one patient with fungal keratitis , 2 patients with pseudomonal keratitis , and 3 patients with polymicrobial infections underwent evisceration to eradicate the infections .
treatment for microbial keratitis the mean hospital stay was 13.7    11.5 days .
longer hospital stay was correlated with previous steroid use , ocular and systemic diseases , longer interval between symptom presentation and admission , previous ocular surgery , large ulcer size , fungal infection , ntm infection , poor visual acuity at presentation , old age , and surgery during admission ( all p  <  0.05 by simple linear regression ) . in multiple linear stepwise regression analysis ,
4 factors including previous ocular surgery , large ulcer size , ntm infection , and surgery during admission were associated with longer hospital stays ( table 6 ) .
during the 10-year study period , 558 patients were included in this study , of which 285 ( 51.1% ) and 273 ( 48.9% ) were male and female , respectively ( table 1 ) .
the mean age of patients was 50.3    22.7 years ( range , 2100 yr ) .
the right eye was involved in 287 patients and the left eye was involved in 271 patients .
the corneal ulcer was small in 192 eyes ( 37.7% ) , medium in 267 eyes ( 52.5% ) , and large in 50 eyes ( 9.8% ) .
the location of the corneal ulcer was central in 238 eyes ( 47.1% ) , paracentral in 206 eyes ( 40.8% ) , and peripheral in 61 eyes ( 12.1% ) .
the presence of hypopyon was noted in 153 eyes ( 33.8% ) . except for laterality , trends for demographics and clinical features were not statistically significant
the most common risk factor was contact lens wear ( 31.4% ) , followed by systemic and ocular diseases ( 26.3% ) , trauma ( 23.5% ) , and previous ocular surgery ( 12.7% ) ( table 2 ) .
a total of 54 patients ( 12.7% ) had at least 2 predisposing factors for corneal ulcers .
materials causing ocular trauma included plant ( n  =  24 ) , iron ( n  =  16 ) , mud ( n  =  5 ) , chemical ( n  =  4 ) , wood ( n  =  3 ) , and unidentified sources ( n  =  48 ) .
lagophthalmos ( n  =  16 ) and dry eye ( n  =  14 ) were the most common ocular surface diseases .
the trend test showed that during the 10-year study period , the proportion of patients wearing contact lenses and with trauma increased ( p  =  0.011 and p  =  0.035 , respectively ) , and the rate of previous ocular surgery decreased ( p  =  0.027 ) .
two hundred thirty - eight ( 42.7% ) patients were administered topical antibiotics before referral , and 88 patients had negative culture results . regarding isolates , 210 bacterial isolates ( 59.9% ) , 62
fungal isolates ( 17.6% ) , 8 nontuberculous mycobacteria ( ntm ) isolates ( 2.3% ) , and 2 acanthamoeba isolates ( 0.6% ) were identified ( table 3 ) .
seventy - one patients had polymicrobial infections ( 20.1% ) . among bacterial isolates , gram - negative bacteria ( 37.4% ) were more common than gram - positive bacteria ( 22.1% ) .
the most commonly isolated bacterium was pseudomonas aeruginosa ( 28% ) , followed by coagulase - negative staphylococcus ( cns , 5.4% ) and staphylococcus aureus ( 4.5% ) .
the percentage of serratia marcescens decreased significantly ( p  =  0.033 ) ; the identified organisms did not change over 10 years .
isolated organisms in microbial keratitis table 4 lists isolated organisms from patients with different risk factors for microbial keratitis .
gram - negative bacteria , particularly p. aeruginosa , mainly accounted for contact lens - related keratitis ( 52.9% ) .
keratitis associated with ocular and systemic diseases was mainly caused by bacteria ( 33.8% and 29.4% for gram - positive and gram - negative bacteria , respectively ) .
all patients were initially treated with empiric antimicrobials , which were adjusted on the basis of the clinical response and the results of the drug susceptibility test .
medical treatment was successful for patients with gram - positive bacterial infections ( 62.8% ) , gram - negative bacterial infections ( 78% ) , ntm infections ( 75% ) , acanthamoeba infections ( 100% ) , and polymicrobial infections ( 74.6% ) ( table 5 ) .
surgical procedures included amniotic membrane transplantation , patch graft , lamellar keratectomy , penetrating keratoplasty , and evisceration .
one patient with fungal keratitis , 2 patients with pseudomonal keratitis , and 3 patients with polymicrobial infections underwent evisceration to eradicate the infections .
treatment for microbial keratitis the mean hospital stay was 13.7    11.5 days .
longer hospital stay was correlated with previous steroid use , ocular and systemic diseases , longer interval between symptom presentation and admission , previous ocular surgery , large ulcer size , fungal infection , ntm infection , poor visual acuity at presentation , old age , and surgery during admission ( all p  <  0.05 by simple linear regression ) . in multiple linear stepwise regression analysis ,
4 factors including previous ocular surgery , large ulcer size , ntm infection , and surgery during admission were associated with longer hospital stays ( table 6 ) .
severe infectious keratitis is a leading cause of corneal blindness . optimal clinical practice for the prevention and treatment of microbial keratitis should account for patient - specific risk factors and possible causative organisms in different regions .
in this study , we focused on patients admitted with microbial keratitis ; first , we ensured that only patients with severe infection leading to admission were included in this study , and second , we used the same ( or as similar as possible ) criteria as used in a previous report conducted at another university hospital in northern taiwan between 1992 and 2001 to provide updated regional epidemiological information .
our findings showed that contact lens wear remained the leading risk factor for inpatient microbial keratitis , and the trend increased significantly over the 10-year study period ; p. aeruginosa was the most common causative organism . in the current study , risk factors for microbial keratitis from 2003 to 2012 were contact lens wear , ocular and systemic diseases , trauma , and previous ocular surgery , in descending order , which was similar to the results of a previous taiwanese report . in taiwan , the leading risk factor for microbial keratitis was still contact lens wear , which was also reported in the united states , western europe australia , and hong kong .
rattanatam et al found that the number of patients with contact lens - related microbial keratitis decreased in their hospital , suggesting that a higher number of such patients were treated in the community after the introduction of fluoroquinolones .
by contrast , our study demonstrated an increasing trend in the rate of contact lens - related microbial keratitis in our hospital over the 10-year study period ( p  =  0.011 ) . in a prospective , population - based study of contact lens - related microbial keratitis in australia , risk factors for infections included
overnight use , poor storage case hygiene , smoking , internet purchase of contact lenses , less than 6 months wear experience , and higher socioeconomic class ; however , new lens types did not reduce the incidence of infection .
because of the retrospective design of this study , it was difficult to correlate contact lens wearing modalities , hygiene , and other factors with infections ; however , approximately 35.8% of patients had overnight use in our study . wearing contact lenses is popular in taiwan , which is a country with high prevalence of refractive errors , and contact lens - related microbial keratitis has become a public health concern . in 2012 ,
corneal health for care network  to advocate the 3 c 's for contact lens wearers : consulting a physician on how to fit contact lenses correctly ( correct ) , cleaning and maintaining contact lens ( care ) , and receiving regular health check - ups ( check ) .
this campaign is anticipated to facilitate decreases in the rate of contact lens - related microbial keratitis in taiwan . in this study ,
the most common causative organisms were bacteria , followed by fungi ; gram - negative bacteria were more common than gram - positive bacteria , and p. aeruginosa was the most commonly identified isolate .
the spectrum of microorganisms accounting for microbial keratitis differ depending on geographic location , climate , and etiology .
for example , gram - positive bacteria are predominant in temperate climate regions , whereas gram - negative bacteria and fungi are prevalent in tropical regions;pseudomonas species are associated with contact lens - related infections , whereas fungi are related to trauma caused by plants .
the predominance of p. aeruginosa infection in taiwanese studies may reflect both the geographic prevalence of the microorganism and contact lens - related keratitis .
fungi are also crucial causative organisms of microbial keratitis in taiwan ; similarly , this might be due to the geography and climate , and injury caused by plant materials .
notably , 4 of 5 previous studies in europe and taiwan investigating microbiological findings of hospitalized patients with microbial keratitis have reported that gram - negative bacteria are the most common causative organism .
this finding might suggest that microbial keratitis caused by gram - negative bacteria , particularly pseudomonas species , tends to be severe and progresses rapidly , thus requiring admission . in the current study ,
medical treatment was successful in 69.5% of patients ; more than half of the patients with fungal keratitis required additional surgical interventions to control infections .
medical treatment of fungal keratitis , particularly deep - seated infections , is often unsatisfactory because of delayed diagnosis , inadequate drug penetration , and slow response to therapy . surgical intervention to remove infectious elements and necrotic tissue may increase drug penetration and shorten the clinical course .
however , therapeutic corneal transplantation and even destructive surgery may be indicated for severe keratitis with a poor response to medical therapy or when severe complications supervene .
long hospital stay also has effects on financial resources , staffing , and turnover rate of beds in the public health service . in this study ,
the mean hospital stay was 13.7 days , and longer hospital stays were associated with previous ocular surgery , large ulcer size , ntm infection , and surgery during admission .
a study of hospitalized patients with infectious keratitis in new zealand reported that longer hospital stay was associated with the presence of hypopyon , larger ulcers , previous ocular surgery , and poor visual acuity .
as expected , large ulcers or surgery during admission prolonged hospital stay . older age and longer duration from symptom onset to diagnosis
were noted in patients with previous ocular surgery ( data not shown ) , which might explain the relationship between longer hospital stay and previous ocular surgery .
ntm has a relatively slow growth rate , and the infection can mimic that caused by other pathogens .
thus , the delay in diagnosis and treatment of ntm infections might prolong hospital stay .
morbidities caused by microbial keratitis can be assessed on the basis of surgical intervention , hospital stay , and visual loss . in this study
, we did not analyze the predictors for poor visual outcome in microbial keratitis because of visual assessments with variable follow - up intervals .
however , the study in new zealand reported that longer hospital stays were associated with poor visual acuity both at presentation and final assessment .
we included cases with both positive and negative culture results , and we could not exclude the possibility that cultured isolates were contaminated .
because our patients were admitted to a tertiary referral hospital in taiwan , the results can not be generalized . in conclusion ,
p. aeruginosa was the most common causative organism , and contact lens wear was the most common risk factor for microbial keratitis ; there was a significant increase in the percentage of contact lens - related keratitis during the 10-year study period in taiwan .
the majority of patients with microbial keratitis were cured through medical treatment , but a high proportion of patients with fungal keratitis required surgical interventions .
microbial keratitis has the potential to cause devastating visual impairment and major costs to the public health system ; our findings provide updated information and facilitate future prevention and treatment of microbial keratitis in taiwan .
 abstractwe conducted a retrospective , cross - sectional study to analyze predisposing factors , clinical features , and microbiological characteristics of patients with microbial keratitis hospitalized over 10 years.the medical records of 558 patients who were diagnosed with microbial keratitis and admitted to chang gung memorial hospital ( cgmh ) , a referral center in taiwan , from january 1 , 2003 to december 31 , 2012 were reviewed . 
 demographics , predisposing factors , isolated organisms , treatment , and hospital stay were recorded . 
 yearly trends were tested using a linear - by - linear association.contact lens wear was the most common predisposing factor ( 31.4% ) , followed by ocular and systemic diseases ( 26.3% ) and trauma ( 23.5% ) . 
 contact lens - related infectious keratitis increased year by year ( p  =  0.011 ) . 
 pseudomonas aeruginosa was the most commonly isolated organism ( 28% ) , followed by fungi ( 17.6% ) and coagulase - negative staphylococcus ( 5.4% ) . except for serratia marcescens , 
 the identified organisms did not change over 10 years . 
 most bacterial infections were controlled using antimicrobial treatment , but more than half of patients with fungal keratitis required surgical interventions . 
 the mean hospital stay was 13.7    11.5 days . 
 previous ocular surgery , large ulcer size , nontuberculous myycobacteris infection , and surgery during admission were related to prolonged hospital stay.in taiwan , contact lens - related pseudomonal keratitis remained the most common cause of microbial keratitis in patients hospitalized from 2003 to 2012 . 
INTRODUCTION
METHODS
RESULTS
Demographics and Clinical Features
Predisposing Factors
Microbiological Analysis
TREATMENT
DISCUSSION