Prob­lem with the la­bel of ‘su­per­bug’

Baltimore Sun - - COMMENTARY - By Neil S. Greenspan and Ar­turo Casade­vall

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.

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.

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.

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