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Nocardia transvalensis keratitis: an emerging pathology among travelers returning from Asia
- Elodie Trichet†1,
- Stéphan Cohen-Bacrie†2,
- John Conrath1,
- Michel Drancourt2 and
- Louis Hoffart†1Email author
© Trichet et al; licensee BioMed Central Ltd. 2011
Received: 28 January 2011
Accepted: 31 October 2011
Published: 31 October 2011
The incidence rate of Nocardia keratitis is increasing, with new species identified thanks to molecular methods. We herein report a case of Nocardia transvalensis keratitis, illustrating this emerging pathology among travellers returning from Asia.
A 23-year-old man presented with a 10-week history of ocular pain, redness, and blurred vision in his right eye following a projectile foreign body impacting the cornea while motor biking in Thaïland. At presentation, a central epithelial defect with a central whitish stromal infiltrate associated with pinhead satellite infiltrates was observed. Identification with 16S rRNA PCR sequencing and microbiological culture of corneal scraping and revealed N. transvalensis as the causative organism. Treatment was initiated with intensive topical amikacin, oral ketoconazole and oral doxycycline. After a four-week treatment period, the corneal infiltrate decreased so that only a faint subepithelial opacity remained.
Nocardia organisms should be suspected as the causative agent of any case of keratitis in travelers returning from Asia. With appropriate therapy, Nocardia keratitis resolves, resulting in good visual outcome.
Nocardia spp. keratitis is an aggressive ocular infection, typically following a corneal trauma. The diagnosis is often delayed, which can lead to a corneal scar . While the most commonly identified agents have been Nocardia asteroides and Nocardia brasiliensis in the pre-molecular area , new species are now identified thanks to molecular methods and later two species are now rarely identified as clinical isolation. Herein, we report one case of Nocardia transvalensis keratitis, illustrating this emerging pathology among travelers returning from Asia.
In the case reported herein, temporal evidence links the infection and the airborne dust that the patient suddenly felt in his eye while motorbiking in Thailand. Moreover, the patient was not a contact-lens wearer, and he did not have any history of ocular problems. We thus concluded that the patient acquired the infection in Thailand. In this patient, N. transvalensis infection was firmly documented by culture and subsequent sequence-based identification. This second reported case of N. transvalensis ocular infection  indicates that N. transvalensis must be added to the list of Nocardia species associated with infectious keratitis [2, 4]. Of a total of 73 reported cases of Nocardia spp. keratitis over the last five years, 67 (92%) have been clearly acquired in individuals with direct links to Asia [2, 3, 5–16]. Whereas Nocardia spp. keratitis is a well-described clinical entity in Asia , it is seldom diagnosed in countries outside Asia. A recent visit to Asia therefore provides a clue for clinical diagnosis while waiting for PCR-based confirmation. Laboratory techniques have to be used to analyze every case of infectious keratitis because simple microscopic examination may mistakenly identify the case as fungal keratitis when the histopathology reveals acute-branching septate hyphae similar to those found in fungi. The most frequently noted predisposing factor for Nocardia keratitis is trauma, with surgery being the second most common factor. A few cases of Nocardia keratitis have also been reported in contact lens wearers, after refractive surgery and after implantation of intracorneal ring segments [1, 17].
Topical amikacin is commonly recommended to treat Nocardia keratitis  based on its in vitro antibacterial activity against Nocardia organisms , its demonstrated corneal penetration and its safety profile . Several authors previously reported that the species N. transvalensis in fact comprises of an heterogeneous spectrum of organisms including both amikacin-susceptible and amikacin-resistant organisms, a hallmark of the N. transvalensis complex also incorporating the two newly described reported N. blacklockiae and N. wallacei . In the patient herein reported, intensive tropical application resulted in complete resolution of the infection. One previously published case of N. transvalensis keratitis showed a decreased sensitivity to amikacin . In fact, amikacin susceptibility and resistance have been determined on the basis of amikacin concentration achievable in serum during systemic Nocardia infections; as for Nocardia keratitis, amikacin is used as a topical antibiotic, achieving local concentrations far higher than those achievable during parenteral administration. While amikacin susceptibility profile could be used for the identification of Nocardia isolates, it is not useful for the topical treatment of Nocardia keratitis.
The rate of travel of Europeans to tropical regions in Asia for vacation or business has increased dramatically; more than 8 million travelers flew back from Asia to France in 2009. Nocardia organisms should be suspected as the causative agent of any case of keratitis in travelers returning from Asia, especially those travelers who experienced a soil-borne corneal trauma and those who are contact lens wearers. Molecular tools may help in making a rapid diagnosis.
Written informed consent was obtained from the patient for publication of this report.
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