Antibiotic Overuse – how much does it matter?

Thursday 1/17/08

Spread of resistance

Antibiotic pressure

Human to human transmission

Mechanisms by which Antibiotic use can induce resistance

Lipsitch & Samore EID 2002

Antibiotic selection of resistant mutants

Ab treatment => outgrowth of resistant subpopulations or acquire de novo resistance

Antibiotic pressure => increased load or resistant bacteria

By eradicating a susceptible strain making the host more susceptible to new acquisition of

strains

Indirect effect – reduced transmission of susceptible strains to other susceptible hosts

Antibiotics are drugs with externalities (like pollutants)

• By treating an individual with antibiotics – other individuals in the society are influenced

• Antibiotic treatment – maybe beneficial for an individual but deleterious for society.

Types of studies that examine the relationship between Ab use and Ab

resistance• Ecological studies

• Individual level studies– Case-control– Quasi-experimental studies– Longitudinal studies

• Mathematical models

Total Ab use in 26 European countries in 2002/ Goosens et al. Lancet 2005

Total Ab use in 2004 / Goosens CID 2007

Correlation between Pen use and PRSP / Goosens et al. Lancet 2005

Do all antibiotic classes induce resistance similarly? The pneumococcus paradigm / Dagan et

al. PIDJ 2006

Antibiotic use as a risk factor for MRSA (in ED) / Moran et al. NEJM 2006

Antibiotic consumption and MRSA, an ecologic study (EID 2004)

FQ use and FQ-R MRSA and E. coli (community and HA)/ MacDougall et al. CID 2005

Is there overuse/non-judicious use of antibiotics?

• ~50% of Ab prescriptions are non-judicious

• What is non-judicious use?– Ab for viral infections– Wrong dose– Wrong duration– Wrong Ab class – Broad ab class when narrow is as good

Why is there non-judicious use?

• Lack of knowledge

• Patient demand

• Uncertainty (of Dx, of risks and benefits)

• Medico-legal issues – fear from lawsuit

• Low awareness to Ab resistance problem

Effect of antibiotic use in agriculture

• Over 50% of Ab produced in US are used for agricultural purposes

• Use for growth promotion and treatment of food animals

• FQ used to treat chicken:– Identical strains of FQ-R Campylobacter found in

raw chicken as those in humans

Agriculture use and Ab resistance: Quantifying the effect

• Animal use can be a selective force responsible for the assembly of resistant gene clusters

• Reservoir for resistance-encoding plasmids (or other genetic elements) in animal commensal bacteria

• Bacteria that are shared by food animals and humans (VRE).

Is it not too late?

• Regulation now may have little or no effect.

• Waiting for conclusive evidence may result in a missed opportunity to prevent damage!