Culture‐positive shigellosis cases are epidemiologically different to culture‐negative/PCR‐positive cases

Abstract

Objective: To review the epidemiological differences between culture‐positive and culture‐negative (but ipaH PCR‐positive) cases of shigellosis in Sydney Local Health District (SLHD), NSW, to inform whether changes to the national case definition for shigellosis are required. Methods: An audit of all cases of shigellosis (culture‐positive vs. culture‐negative/PCR‐positive) in SLHD from 1 January 2013 to 30 June 2015 was conducted and demographic, clinical and risk factors were analysed and compared between these groups. Results: Of the 148 shigellosis cases notified to SLHD, 122 cases (85 culture‐positive vs. 37 culture‐negative) were included for analysis. Culture‐positive cases were more likely than culture‐negative/PCR‐positive cases to have experienced at least three symptoms (OR 3.18, 95%CI 1.3–7.5), been hospitalised (OR 4.2, 95%CI 1.4–13.2), and have had men‐who‐have‐sex‐with‐men exposure identified as the source of their infection (OR 28.7, 95%CI 6.2–132.6). Conclusions: This study has identified that culture‐positive vs. culture‐negative/PCR‐positive shigellosis cases in NSW differ by clinical severity and risk factors for infection. Implications for public health: The study findings warrant further research to determine the true diagnostic prevalence of Shigella in the culture‐negative/PCR‐positive group in the Australian context, in order to inform further changes to the national case definition for shigellosis.

Incidence, clinical implications and impact on public health of infections with Shigella spp. and entero-invasive Escherichia coli (EIEC): results of a multicenter cross-sectional study in the Netherlands during 2016–2017

“…Similar to others, we found that culture-negative cases were less likely to report MSM contact, more likely to report traveling and have a longer symptomatic period [31, 33]. Others explained that their culture negative cases reported higher travel rates because they are more likely to be infected by EIEC [33]. However, this explanation is not applicable to our study, as there is high certainty that EIEC infections were not included in our culture-negative group, because they were molecularly typed as S. flexneri or S. sonnei with a specificity of at least 98%.…”

“…Similar to others, we found that culture-negative cases were less likely to report MSM contact, more likely to report traveling and have a longer symptomatic period [31, 33]. Others explained that their culture negative cases reported higher travel rates because they are more likely to be infected by EIEC [33].…”

“…We suggest that laboratory confirmation might have been requested later in the course of the disease for travelers, reducing the chance of obtaining an isolate [23]. This is supported by the observation that the time between onset of disease and sample collection was longer for culture-negative cases in the earlier studies [31, 33]. Unfortunately, in our study, data about time of onset of disease was not available.…”

“…Additionally, public health authorities struggle with the control of shigellosis cases identified with molecular techniques alone, because the impact of these cases for patients and public health is also not well defined [31, 32]. Two studies have looked at differences in case demographics, risk factors, and disease outcomes of shigellosis in culture-positive cases versus culture-negative cases [31, 33]. However, in both studies the proportion of EIEC infections amongst the culture-negative cases was unknown, and in one of the studies the data was biased because laboratory testing was unevenly distributed between laboratories that used either culture methods or molecular methods [31, 33].…”

Epidemiology of Shigella infections and diarrhea in the first two years of life using culture-independent diagnostics in 8 low-resource settings

“…An 11-fold higher detection of Shigella was observed with qPCR compared to culture, including a 3-fold increase for Shigella -attributable dysentery. While higher sensitivity of culture among more severe cases has been previously noted [ 23 ], culture still missed the majority of cases of Shigella diarrhea, severe diarrhea, and dysentery, and culture had the lowest sensitivity among young children who are at highest risk for poor outcomes. These results highlight the need for more sensitive diagnostic tools.…”