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Jesse M Smith, Marc Mathias, Alan Palestine; The influence of needle gauge and infection source on vitreous aspirate cultures. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4181.
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In infectious endophthalmitis, culture of a vitreous sample is important in identifying the causative organism as well as establishing antibiotic sensitivities. The Endophthalmitis Vitrectomy Study (EVS) reported a 69% microbiologic yield using 22-27 gauge needles for vitreous tap or a 20-gauge vitrectomy cutting instrument for vitreous biopsy. We hypothesized that smaller needle gauges do not reduce this yield. We further hypothesized that the yield from vitreous tap in cases of endogenous endophthalmitis is significantly lower than in non-endogenous cases.
We analyzed 14 years of data from a tertiary referral center and a county hospital. Criteria for inclusion were: evidence of presumed infectious endophthalmitis, defined as the presence severe intraocular inflammation, vitritis, or characteristic fundus lesions. Endogenous endophthalmitis was diagnosed in the setting of bacteremia, fungemia, or intravenous drug abuse without recent ocular surgery or trauma. Vitreous samples were obtained by introducing a needle through the pars plana and aspirating at least 0.1cc of vitreous. Mechanized vitrectomy was not used to obtain samples. Yield from a vitreous sample was considered positive if a plausible organism was cultured.
Forty-six cases were included in the study. Ten cases were endogenous endophthalmitis, while 36 cases were a mix of postoperative, posttraumatic, post-intravitreal injection, and miscellaneous patients. A 25-27 gauge needle was used to obtain a vitreous sample in 36 cases, and a 30 gauge needle was used to obtain a vitreous sample in 10 cases. A positive microbiologic culture was obtained in 31% of vitreous taps using a 25-27 gauge needle and in 80% of taps using a 30 gauge needle (p<0.05). A positive culture was obtained in 50% of all non-endogenous cases, while a positive result was obtained in 0 cases of endogenous endophthalmitis (p<0.01). An organism was identified in 80% of blood cultures done in endogenous cases.
Use of a smaller needle in obtaining vitreous samples in endophthalmitis did not lower the microbiologic yield. A positive microbiologic yield was significantly less likely in cases of endogenous endophthalmitis compared to non-endogenous cases. Vitreous tap as a method for identifying the causative organism in endogenous endophthalmitis was of limited utility in general and is inferior to standard blood culture techniques.
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