Is there an association between trimethoprim-sulfamethoxazole use as prophylaxis and multi-drug resistant non-typhoidal salmonella? A secondary data analysis of antibiotic co-resistance surveillance data in South Africa - 2003-2005
Date
2011-03-10
Authors
Nanoo, Ananta
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Abstract
Introduction
Given the increasing prevalence of non-typhoidal salmonella in humans, especially as an
opportunistic illness associated with HIV, enhanced surveillance for non-typhoidal salmonella
(NTS), including screening for antibiotic resistance, is conducted annually in South Africa. We
aimed to determine whether there is an association between trimethoprim-sulfamethoxazole
(TMP-SMX) prophylaxis and multi-drug resistant NTS infection, to establish whether various
factors modify the relationship between TMP-SMX resistance and invasive NTS infection, to
examine whether these associations vary by province, and to quantify the resistance rates of NTS
to a range of antibiotics.
Methods
This study was a secondary analysis of enhanced surveillance data on NTS collected between
2003 and 2005. We used descriptive methods to assess the prevalence of NTS by year, province
and serotype, and to determine the prevalence of four MDR patterns. Univariate and multivariate
regression models were used to investigate the relationships between TMP-SMX prophylaxis
and MDR NTS. Univariate logistic regression was used to assess the relationship between
invasive NTS and TMP-SMX resistance.
Results
TMP-SMX prophylaxis is associated with the ACKSSuT pattern (OR 1.91, 95% CI 1.14 – 3.19,
p=0.0080) and the AKSSuT MDR pattern (OR 2.00, 95% CI 1.26 – 3.15, p=0.0015). Being on
TMP-SMX prophylaxis is associated with an increased odds of having at least one of the four
MDR patterns investigated (OR 1.43, 95% CI 1.00 – 2.04, p=0.0388). We also found high rates
of resistance to all antibiotics tested except for ciprofloxacin and imipenem. The highest
resistance rate was observed for sulfamethoxazole (>75.85%). S. enterica Isangi isolates showed
the highest levels of resistance, with 94.43% having at least one MDR pattern. Other factors
significantly associated with MDR NTS were ESBL production, prior treatment with antibiotics,
HIV status and resistance to TMP-SMX.
Discussion and conclusions
Isolates from patients on TMP-SMX prophylaxis were associated with an increased odds of
having the ACKSSuT and AKSSuT MDR patterns, not taking into account other explanatory
factors. These associations did not remain significant when possible confounders were taken into
account. Despite the threat of increased multi-drug resistance, TMP-SMX prophylaxis remains
important in certain clinical settings.
Description
MSc (Med), Epidemiology and Biostatistics, Faculty of Health Sciences, University of the Witwatersrand
Keywords
multi-drug resistance, antibiotic resistance, non-typhoidal salmonella