Isolates from Patients with Noninvasive Listeria monocytogenes: Are They Important?

BACKGROUND: From 2004–2015, CDC received 82 reports of patients with Listeria monocytogenes (Lm) cultured from non-sterile sites. Whereas invasive listeriosis (Lm isolated from typically sterile sites) is nationally notifiable and well described, information about patients with “noninvasive” Lm (isolated from other sites) is limited to a small number of case reports. We summarize the demographic and clinical characteristics of a convenience sample of patients with noninvasive Lm and compare to patients with invasive Lm reported through routine surveillance. METHODS: The Listeria Initiative (LI) is a national surveillance system that collects demographic, clinical, laboratory, and food exposure information on laboratory-confirmed listeriosis cases in the United States. While not nationally notifiable, public health agencies can also submit similar information to LI for patients with noninvasive Lm. We reviewed all reports to LI from 2004–2015 and used a standardized approach to characterize isolate sources as invasive or noninvasive. We then compared demographic and clinical factors between patients with invasive and noninvasive Lm using Fisher’s exact and Wilcoxon rank-sum tests. RESULTS: The most common sources of noninvasive isolates (n = 82) were skin or soft tissue (n = 35, 43%), urine (n = 19, 23%), and stool (n = 17, 21%). Compared with patients with noninvasive Lm, patients with invasive Lm (n = 4599) were more likely to be older than 65 years (66% vs. 54% P = 0.03), to be associated with an outbreak (17% vs. 7%, P = 0.02), to be hospitalized (92% vs. 54%, P < 0.01), and to die (20% vs. 4%, P < 0.01). CONCLUSION: This is the first review of patients with noninvasive Lm using US LI surveillance data. Patients with invasive Lm were older and more likely to be associated with an outbreak, hospitalization, or death when compared with patients with noninvasive Lm. The reasons that patients with noninvasive Lm have a less severe clinical course are not well understood; however, the frequency of hospitalizations and deaths in patients with noninvasive isolates indicates their clinical relevance and public health significance. DISCLOSURES: All authors: No reported disclosures.