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Volume 18, Number 2—February 2012


Plesiomonas shigelloides Infection, Ecuador, 2004–2008

Juan C. Escobar, Darlene Bhavnani, Gabriel Trueba, Karina Ponce, William Cevallos, and Joseph EisenbergComments to Author 
Author affiliations: University of Michigan, Ann Arbor, Michigan, USA (J. Eisenberg, D. Bhavnani); Universidad San Francisco de Quito, Quito, Ecuador (G. Trueba, W. Cevallos, K. Ponce, J.-C. Escobar)

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RRs and bootstrapped 95% CIs for single infections and co-infections with Plesiomonas shigelloides, Ecuador, 2004–2008*

Co-infection RRSingle P.shig (95% CI) RRCo-Infection (95% CI) RRCrude (95% CI) RRMH-Pooled (95% CI) Wald test for heterogeneity p value
Any pathogen 1.5 (0.9–2.2) 5.6 (3.5–9.3) 2.6 (1.9–3.5) 2.7 (1.9–3.6) 32.1 <0.001
Rotavirus 1.5 (0.9–2.2) 16.2 (5.5–62.3) 1.7 (1.1–2.5) 1.9 (1.2–2.9) 61.8 <0.001
Giardia spp. 1.5 (0.9–2.2) 2.1 (1.0–3.9) 1.5 (1.0–2.2) 1.6 (1.1–2.3) 1.3 0.2
Escherichia coli/ shigellae 1.5 (0.9–2.2) 13.8 (3.3–69.3) 1.6 (1.1–2.4) 1.7 (1.1–2.6) 32.8 <0.001

*RR, risk ratio. RRcrude = the unadjusted RR and RRMH-pooled is the pooled Mantel-Haenszel RR ratio estimate. The Wald test assesses whether the strata RRSingle P.shig and RRco-infection differ. Because of the clustered study design and the unequal sampling probabilities of controls, we chose not to use logistic regression models. Instead, we applied a nonparametric approach by using sampling weights to estimate RRs, as one would for a cohort study. We bootstrapped 1,000 samples from the original dataset, and with each new sample, we estimated the RR associated with single infection and co-infection. The lower 0.025 and upper 0.975 percentiles of the bootstrap distribution are reported as 95% CIs. Statistical analyses were conducted by using R version 2.11.1 (

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