Although uncommon, infectious keratitis in children is a condition that leads to an imminent risk of amblyopia and/or permanent visual loss and because of this the cost per case is very high .
Children may be poor historians and/or may not complain of ocular pain. Keratitis diagnosis and treatment may be delayed by parents, or by primary care physicians confusing keratitis with the less severe conjunctivitis, especially if the cornea is not severely affected and the infiltrate not macroscopically obvious. This may be reflected in our study where the mean time to diagnosis was almost 2 weeks. This fact may also explain the poor visual outcomes and highlights the importance to educate parents and primary care personnel in the importance of immediate referral whenever the cornea may be involved.
In our series, a history of trauma was the major predisposing factor, present in approximately one quarter of the cases (25%). This result is consistent with multiple microbial keratitis studies involving children where ocular trauma has been associated in up to two thirds of the cases. (26–58.8%) [2, 11–13]. Corneal trauma disrupts the protective mechanism of the corneal epithelium, facilitating bacterial adhesion and accelerating penetration and replication of microorganisms [12, 13]. Children are less careful than adults and do not understand the harm that is associated with dangerous objects. Plants, metals, plastic parts, fireworks and pencils may cause ocular trauma .
In our study, 15.6% of patients had a history of wearing contact lenses. Interactions between contact lens and ocular surface generated by chronic or improper contact lens wear such as overnight wear, may produce epithelial defects that predispose the wearer to bacterial adhesion [14, 15]. Exposure to contaminated disinfectant solutions and biofilm formation are additional mechanisms that can cause corneal infection [16, 17]. Although statistics are lacking, pediatric contact lens wear may be more common in populations where high myopia is prevalent and/or orthokeratology is popular. In our population, orthokeratology is rarely used and but its use should be cautiously advised specially in children with other risk factors for infections (pediatric rosacea, recurrent blepharitis) [6, 18].
The influence of systemic diseases and malnutrition on the wound healing process should be considered as a predisposing factor for microbial keratitis in children [19, 20]. A wide variety of factors such as low socioeconomic status, incomplete immunization profile and systemic diseases, including hypoxic encephalopathy, pulmonary stenosis, protein-energy malnutrition, multiple congenital anomalies and prematurity have been associated with severe microbial keratitis in children [2, 12, 13, 21, 22]. Jhanji and co-authors recently reviewed the role of immunization and malnutrition in corneal ulcers in children 5 years or younger . The severity of protein-energy malnutrition was related significantly to the occurrence of bilateral infection, to an incomplete immunization scheme and poor socioeconomic status, however this study did not address the confounding between these variables. In our study, we found 3 cases with associated systemic diseases. Two children had psychomotor retardation and malnutrition, and the other had chronic cardiopulmonary disease.
Local predisposing factors for infectious keratitis were found in 16 cases (50%), which included chronic steroid use, ocular rosacea and previous ocular surgeries, congenital facial paralysis and previous herpetic infection. These factors, as well as dry eye, exposure keratopathy and eyelid abnormalities act as facilitators of corneal infection [11, 13].
Regarding microbiological profile, we found that cultures were positive in 34% of cases, a value that was lower than those reported in other studies (48% to 87%) [20, 21, 23]. Self-prescribed antibiotic, microorganisms with slow growth on culture media, viral causes of keratitis, improper corneal sampling, and the inherent difficulty in getting corneal samples from pediatric patients may account for the low positivity rate observed in our study. The higher rates of culture positivity reported in the other studies, may also be explained by their use of general anesthesia or deep sedation for corneal scrapings in uncooperative patients [20, 21, 23].
As shown previously by other authors, Gram-positive microorganisms are the main etiological agents of infectious keratitis in children [2, 7]. Over the years, an increased incidence of keratitis caused by coagulase-negative Staphylococcus has been reported, [12, 13, 20–23] and many studies consider coagulase-negative Staphylococcus as an important cause of endophthalmitis [24–26]. The antibiotic susceptibility of coagulase-negative Staphylococcus isolates is unpredictable, and that multi-resistance to antibiotics is common. Therefore, an antibiogram should be performed in the clinically significant ocular infections that arise from these organisms .
We observed a high resistance of Staphylococcus spp. to the antibiotics known for their action against gram-positive organisms, including sulfamethoxazole, first-generation cephalosporins and oxacillin; the latter used as a surrogate marker for methicillin-resistant organisms. A hundred percent of these cases were susceptible to gentamicin, and 80% to ciprofloxacin and vancomycin. Alternatively; Streptococcus spp. isolates were sensitive to the majority of antibiotics. Resistance to multiple antibiotics was seen in 80% of Staphylococcus spp. and in 25% of Streptococcus spp. isolates. Prolonged antibiotic therapy is known to promote the adaptation of organisms and development of specific cross-resistance mechanisms although knowledge of the local resistance trends in ophthalmic specimens is mandatory to provide a prompt and effective treatment [27, 28].
In general, fluoroquinolones susceptibility profile was good across our series of positive cultures, making this class of antibiotic suitable for empiric treatment that may be modified according to the antibiogram results. Although in our setting resistance is uncommon, sites where it’s use is widespread in healthcare, resistance is a concern [29, 30].
Finally, as previously reported , vancomycin is an effective anti-staphylococcal drug that is rarely associated with resistance, hence, it is important that this drug be reserved for treating infections that are resistant to other anti-staphylococcal antibiotics or in cases of severe corneal infections. In this report we encountered a Staphylococcus epidermidis strain that was resistant to vancomycin, which suggests the existence of some strains with complex resistance mechanisms in our environment.
The findings of this study should be interpreted cautiously. This study is limited by its small sample size and is subject to selection bias since it was performed at a tertiary referral eye care center, so the results here presented cannot be extrapolated to the general population. Nevertheless, our results strengthen the body of knowledge around infectious keratitis in children and contribute to a better understanding of microbial corneal ulcers in the pediatric patient, in the hope of improving their visual outcome.