Microbiological culturing is the current gold standard for identifying pathogens but recent advancements in polymerase-chain reaction (PCR) and whole-genome sequencing (WGS) provide a more sensitive and specific means of diagnosis.[45,46] A recent review found that pathogens were detected by WGS in 36% of culture-negative endophthalmitis cases. The most common organism isolated was S. epidermidis, which could explain the similarity in prognosis between cases caused by this organism and culture-negative cases. Real-time PCR allows for identification of certain pathogens within hours, which could indicate prognosis if bacteria associated with more severe infections were identified. PCR, like cultures, is also significantly less sensitive in aqueous humor compared with vitreous fluid. WGS also identified torque tenovirus in 49% of cases of postprocedural endophthalmitis, and 60% of culture-negative cases. Increased levels of this virus are believed to indicate decreased immune function, which could explain the increased severity of infection and risk of secondary vitrectomy in eyes in which it was isolated.[47,48]
Another role for WGS could be in diminishing the need for vitreous tap and aspiration to obtain microbiologic cultures. Although anterior chamber paracentesis yields a lower culture-positivity rate compared with vitreous aspiration, this may not hold true for PCR and WGS. Furthermore, vitreous aspiration during a vitreous tap may be associated with risk for retinal tears, detachments, zonular trauma, and choroidal detachments, which could be avoided if anterior chamber paracentesis could be substituted. Prior studies suggest that microbiologic cultures rarely change management and their utility is more in determining final visual prognosis, as culture-positive cases are more likely to have worse visual outcomes than culture-negative cases. In addition, patients with postcataract endophthalmitis are often referred to large care centers because of current guidelines, which recommend that vitreous samples should be processed within two hours of collection. Delayed WGS or PCR testing could allow retina specialists in rural settings to administer immediate intravitreal antibiotics and perform anterior chamber paracentesis, after which the sample could be sent to a laboratory with testing capabilities. Regardless of the causative pathogen, it is imperative to administer immediate antibiotics in cases of presumed infectious endophthalmitis. As stated above, culture results very rarely affect antibiotic treatment, and obtaining microbiologic cultures should not delay initiation of antibiotic treatment.
Curr Opin Ophthalmol. 2021;32(1):62-68. © 2021 Lippincott Williams & Wilkins