Friday, February 25, 2011

Resistant Salmonella Concord from Ethiopia

APUA chapter advisor for sub-Saharan Africa, Dr. Iruka Okeke, Ph.D. and current assistant professor of biology at Haverford College offers her insights on drug-resistant Salmonella Concord infections in Ethiopian adoptees.

There have been a number of worrisome reports in the recent medical literature about drug-resistant Salmonella Concord infections in Ethiopian adoptees.  The reports come from the USA, France, Norway and Denmark, plus a case report from Spain.  Based on global epidemiology of Salmonella, which includes very little information from every country in Africa combined, Salm. Concord is unusual.  The reports about what seems to be an epidemic come from less than two hundred individuals in all over a period of about seven years.  Thus, in a sense, they represent an archetypical example of what University of Virginia’s Richard Guerrant and his co-workers referred to as the ‘eyes of the hippopotamus’  – a mere scratch on the surface of what could be a deeper problem of unimaginable girth. 
 Unfortunately, too much of what we know about pathogens and drug resistance in resource-limited areas still comes from studies performed very distant from those places -  on isolates from returning travelers, or as in the Salmonella Concord case, recent immigrants.  Is it true, as some have suggested, that selection of resistant Salmonella Concord occurs in orphanages that overuse or abuse antibiotics in order to speed up adoption and empty out needed spaces?  Could we nip the problem in the bud by restricting antibiotic use in a few institutions and prescreening international adoptees?  Or is the average Ethiopian child at equal risk of a Salmonella Concord infection, with a significantly lower chance of having it detected and treated appropriately?  And are other, less susceptible individuals transporting Salmonella genomes packed with mobile resistance genes from endemic areas with an efficiency that is analogous to human transport via concord only a decade before?  Should we be developing a Salm. Concord vaccine to deal with the last two possibilities?  Or will the current apparent outbreak burn itself out before we get started?
 Getenet Beyene and co-workers have finally performed a small, but much-needed study to address these vital questions and they’ve done so where it is needed – in Addis Ababa and rural South-West Ethiopia.  The results, published in the January 2011 issue of the Journal of Infections in Developing Countries, are clarifying, if troubling.  Working at Tikur Anbessa Hospital in Addis Ababa and Jimma University Hospital, the researchers looked for Salmonella and other pathogens in the blood of patients with fever and in stool specimens from individuals with diarrhea.  Non-typhoidal Salmonella were isolated from the blood of 26 patients and from the stool of 59 more individuals.  Salmonella enterica serovariety Concord was the most common Salmonella serovar detected, being four times as common as all other Salmonella combined, and it was more invasive than other serovarieties.   The lack of evidence of clonality among the isolates suggests that this is no new epidemic and data from a smaller study published 25 years ago report Salm. Concord from Ethiopia, strongly suggesting that this pathogen has lurked undetected for at least a quarter of a century (Ashenafi and Gedebou, 1985, Trans R Soc Trop Med Hyg 79: 719-721).  Since 1985, Salm. Concord isolates from Ethiopia appear to have become more prevalent, and resistant to more antibiotics.  The isolates in the recent report were resistant to most affordable antibacterial options in Ethiopia.
 Oddly, the literature suggests that this serovar has a narrow geographic range.  However, our perceptions can only be as broad as our vision. There are reasonably good data from Kenya, which suggest that Salm. Typhimurium and Typhi are more important there, but with next to no data from other nearby locations, we cannot be sure that the problem is not extensive. While the endemicity, invasiveness and resistance of Salm. Concord in Ethiopia all give cause for concern, as Beyene et al emphasize in their discussion, the now global problem of multidrug-resistant Salmonella Concord must be addressed from endemic areas.  The very first step is determining where these are, and what exactly are the risk factors for infection.  Everyone is at risk when any part of the world lacks the diagnostic capacity to identify, track and control resistant pathogens. Microbes made the resistance problem a global one decades ago.  To deter them, we need local surveillance worldwide. 
 Iruka N Okeke
Haverford College