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The problem with the ‘superbug’ label

As many as 9,000 Californians are believed to die each year from hospital infections.

Bacterial drug resistance is a major public health problem that potentially affects all of us. Using accurate language is necessary to keep the public optimally informed about this important threat.

In reporting on the problem of bacterial resistance to antibiotics, journalists often refer to the microbes in question as “bugs” with the modifier “super” used as a prefix. We view this choice of terminology as deeply unsatisfactory for several reasons.

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It is almost never specified what extent of drug resistance meets the threshold of “super.” For a given bacterial strain to merit a superlative, how many antibiotics must be resisted? Are two antibiotics enough, or does the use of the modifier require resistance to three or more? How strong does the resistance have to be in terms of the antibiotic concentrations that can be tolerated? Yes, resistance is not all-or-none, it is a quantitative attribute that is assessed in terms of the lowest effective drug concentration.

Sometimes, although not always, when the relevant antibiotics are absent, bacterial strains with a multitude of drug resistance mechanisms are less able to survive and reproduce than strains that lack those mechanisms. This means that some resistant organisms are “super” only in the hospital wards where antibiotics are used and less fit elsewhere. Would Superman have seemed very “super” if he were more capable and more powerful than mere humans only in the setting of a hospital room?

Bacterial strains that possess several mechanisms for inhibiting the effects of antibiotics may not necessarily be more capable of damaging infected individuals. This capacity to cause tissue damage and loss of function is known as virulence. One might assume that a super pathogen would be more virulent, but the infectious agents being called “super” are sometimes only about the same or even less capable of causing harm than other strains that are easier to treat.

A related point is that some of the bacteria that are resistant to multiple drugs are primarily a threat to individuals with immune systems that are functionally deficient in one or more respects. These same pathogens are not a major threat to healthier people with better immune function. Truly “super” pathogens should threaten everyone in a human population, not just the physiologically weaker members.

Perhaps “bugs” is not as objectionable as “super,” but it is still less than satisfactory. This term has a variety of possible meanings and typically no explicit effort is made to clarify which of these are relevant. In addition to referring to microscopic infectious agents, “bugs” can also refer to insects or other small creatures, not to mention software glitches. These other “bugs” (especially certain insects) can, in some cases, transmit disease-causing microorganisms and can also exhibit resistance to chemicals used to kill them, such as the mosquitoes that transmit malaria parasites. Even if we ignore this possible source of confusion and assume it is always clear that microscopic organisms are at issue, it is not clear that “bugs” refers solely to bacteria and not viruses or other pathogens.

So, what criteria should we use to decide what terms are better suited to the task of referring to bacteria that exhibit resistance to multiple drugs? Two criteria are: 1) the words used should accurately describe the bacterial attribute under consideration, i.e. drug resistance, and 2) they should not foster unreliable inferences about other attributes of these same microbes. Microbial drug resistance is definitely a critical variable influencing clinical outcomes but not the only one.

Researchers examined 2,000 soils and found a new class of antibiotics.

Fortunately, there are already more accurate if slightly longer formulations. The simplest formulation is “drug-resistant bacteria” or variations on that wording that replace “drug” with “antibiotic” or “therapy” and substitute “microbe” or “pathogen” for “bacteria”.

More informative wording, already used for drug-resistant mycobacterium tuberculosis, if properly applied, refers to multidrug-resistant (MDR) or extensively drug-resistant (XDR) bacteria that, respectively, exhibit resistance to multiple antibiotics or to all or most relevant antibiotics. MDR and XDR describe the relevant traits without eliciting unreliable inferences about traits that are not necessarily related to drug resistance.

Anyone could one day be at risk of disease caused by these agents. More accurate language in reporting on this medical and public health challenge can therefore benefit everyone.

Dr. Neil S. Greenspan (nsg@case.edu is a professor of pathology at Case Western Reserve University and senior editor of the open access journal “Pathogens and Immunity.” Dr. Arturo Casadevall (acasade1@jhu.edu) is professor and chair of the Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health.

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