Nocardia sp. are Gram-positive, partially acid-fast, aerobic rod-shaped bacteria that rarely cause systemic disease due to low virulence [1–8, 10]. Advances in laboratory speciation techniques have lead to the discovery of newer species, with identification of several other Nocardia sp. capable of infiltrating the cornea [2, 3]. The discovery of Nocardia farcinica is important because of its resistance to several common topical ophthalmic antibiotics [1, 10–13].
Most reported cases of intraocular Nocardia farcinica infection have occurred secondary to haematogenous spread from a primary pulmonary infectious focus in immunocompromised individuals [3–6, 10]. There have been two reported cases of post-operative and post-traumatic endophthalmitis caused from Nocardia farcinica [5, 6].
The genus Nocardia is saprophytes [1–8, 10]. There have been eight documented cases of Nocardia farcinica keratitis [1, 2]. Seven of these cases were reported in a South Indian study, and all occurred secondary to trauma with organic matter [2]. The remaining case of Nocardia farcinica keratitis was contact-lens-related, occurring after semi-permeable rigid contact lenses were cleaned in unchlorinated rainwater [1]. We report the first case of Nocardia farcinica keratitis occurring with the use of extended wear soft contact lenses.
Extended wear soft contact lenses are a well-documented major risk factor for microbial keratitis, due to their interference with the natural defence properties of the ocular surface [14]. It has not commonly been reported as a cause of Nocardia sp. keratitis [1, 2, 15, 16]. However, the larger studies on Nocardia sp. keratitis have been conducted in less urbanised areas, leaving the potential for population bias [2, 16]. Our case adds to the small number of Nocardia sp. keratitis cases where contact lens wear was the most likely predisposing factor [1, 15].
Nocardia sp. keratitis has been reported as presenting with patchy anterior stromal infiltrates—occasionally with feathery borders, stromal hyphae, and wreath-like infiltrates [1, 2, 6, 15, 16]. Keratitic precipitates and endothelial ring deposits have also been documented [2]. The presentation of this case was consistent with these reports but was unusual as there was no history of contamination with plant matter as has been described in other cases of Nocardia farcinica keratitis [1, 2]. Nocardia sp. keratitis mimics the presentation of fungal keratitis and could mislead clinicians to commence empirical treatment with antifungal therapy [1, 2, 15, 17].
Acanthamoeba keratitis is included in the differential diagnosis of Nocardia farcinica keratitis, as both present with marked blepharospasm, photophobia, and wreath-like infiltrates [1, 2]. There has previously been one report of Nocardia asteroides keratitis being successfully treated with polyhexamethylene biguanide, demonstrating that this pool disinfectant could be used as empirical treatment in Nocardia sp. keratitis [2, 15].
Ciprofloxacin 0.3 % eye drops are widely regarded as an empirical treatment for contact-lens-related keratitis due to its efficacy against common causative pathogens [14]. This patient was empirically treated with ciprofloxacin eye drops, and then tobramycin eye drops, another agent commonly used to treat contact lens keratitis [14]. The strain of Nocardia farcinica grown from this patient’s corneal scrapings was resistant to ciprofloxacin and tobramycin. A South Indian study looking at the antibiotic sensitivities of four different Nocardia sp. (N. asteroides, N. farcinica, N. cyriageorgica, and N. otitidiscaviarum) found that Nocardia farcinica was the only species to display complete resistance to gentamicin, tobramycin, and cefotaxime but found that all seven cases were sensitive to ciprofloxacin [18].
Previous reports have found a high level of resistance in Nocardia farcinica to both chloramphenicol and gentamicin [1, 16, 19, 20]. This highlights the importance of testing sensitivities to all potential ophthalmic antibiotics, especially in atypical clinical presentations. This is particularly relevant with Nocardia farcinica, which is resistant to many common topical ophthalmic antibiotic preparations [1, 10, 11, 15–20]. There have been no reports of amikacin resistance in Nocardia farcinica [1, 2, 11, 12, 19, 21, 22]. There have been a few reported cases in the general medical literature of Nocardia farcinica resistance to co-trimoxazole [4, 10, 16, 17].
The role of systemic antibiotics in Nocardia sp. keratitis has not been documented [2, 16]. In this patient, resolution of the epithelial defect and clearing of the corneal infiltrates only occurred after the commencement of oral co-trimoxazole. The high ocular penetration and minimal side effect profile of co-trimoxazole make it beneficial as an adjunct to topical treatment in Nocardia sp. keratitis, based on cultured drug sensitivities [9].
Clinical reactivation of infection occurred with topical steroid use after the epithelial defect had commenced scarring. Reactivation with steroid use in Nocardia sp. has been highlighted before, and they should be used cautiously in Nocardia sp. infections [1, 2].
Nocardia farcinica is a rare cause of keratitis and should be considered as differential diagnoses of contact-lens-related keratitis, post-traumatic keratitis, and clinical pictures suggestive of fungal and Acanthamoeba keratitis. This is the first reported case of Nocardia farcinica keratitis occurring secondary to extended wear soft contact lenses. Nocardia sp. keratitis is a challenge to treat empirically due to high levels of resistance to common topical ophthalmic antibiotics. Despite delayed treatment in this case, the keratitis responded well to a combination of amikacin 2.5 % eye drops and oral co-trimoxazole 160/800 mg BD and long duration of therapy, with a final right eye BCVA of 6/5. This case demonstrates the effectiveness of oral co-trimoxazole160/800 mg BD in treating Nocardia farcinica keratitis, and we recommend considering it as an adjunct treatment based on cultured drug sensitivities.
