Biomedical subjects
Michael Barza
Publications and source records attributed to Michael Barza.
Potential mechanisms of increased disease in humans from antimicrobial resistance in food animals.
There are at least 5 potential mechanisms by which antimicrobial resistance can have adverse effects on human health. The first, called the "attributable fraction," relates to individuals who become infected only because they are taking an antimicrobial agent (for unrelated reasons) to which the pathogen is resistant: the antimicrobial agent, by suppressing their normal microbiota, renders them more vulnerable to infection. A second mechanism involves the linkage of virulence traits to resistance traits so that resistant organisms may be more virulent than susceptible organisms. A third mechanism is that treatment may be rendered ineffective by the choice of a drug to which the pathogens are resistant or may be complicated by the need to use an agent with less desirable attributes than would otherwise be the case. A fourth mechanism is the animal equivalent of the attributable fraction: resistant pathogens acquired by this mechanism in food animals may then be transmitted through the food chain to humans. Last, resistance traits can be acquired by the commensal flora of animals; from this reservoir, resistance traits could find their way through the food chain to commensals and pathogens of humans.
Excess infections due to antimicrobial resistance: the "Attributable Fraction".
Antimicrobial use causes a transient decrease in an individual's resistance to colonization by noncommensal bacteria ("competitive effect") and increases the likelihood of infection upon exposure to a foodborne pathogen. The additional "selective effect" of antimicrobial resistance results in a >3-fold increase in vulnerability to infection by an antimicrobial-resistant pathogen among individuals receiving antimicrobial therapy for unrelated reasons. Combining the increase in vulnerability to infection with the prevalence of taking an antimicrobial agent, it is possible to estimate the attributable fraction, or the number of excess infections that occurred as a result of the unrelated use of an antimicrobial agent to which the pathogen was resistant. Calculations based on estimates of the annual infection rates and attributable fractions of infections with nontyphoidal Salmonella and Campylobacter jejuni suggest that resistance to antimicrobial agents results annually in an additional 29,379 nontyphoidal Salmonella infections, leading to 342 hospitalizations and 12 deaths, and an additional 17,668 C. jejuni infections, leading to 95 hospitalizations.
Morbidity of infections caused by antimicrobial-resistant bacteria.
Antimicrobial resistance can have 2 effects on the outcome of infection: there can be an accompanying change in the virulence of the organism, and there can be a poorer response to treatment because of the empiric choice of an antimicrobial to which the organism is resistant. We have reviewed published studies relating antimicrobial resistance to the outcomes of infection caused by enteric pathogens. The data for Salmonella and Campylobacter infections suggest that antimicrobial-resistant strains are somewhat more virulent than susceptible strains-that is, they cause more prolonged or more severe illness than do antimicrobial-susceptible strains. However, not all studies corrected for possible differences in age and underlying diseases between patients infected by antimicrobial-resistant and -susceptible strains of Salmonella. Two studies of Campylobacter infection suggest that poorer outcomes with antimicrobial-resistant pathogens could be related to the initial choice of an ineffective antimicrobial for treatment. Estimates from various sources indicate that fluoroquinolone resistance, likely acquired from the administration of antimicrobials to food animals, leads to >400,000 excess days of diarrhea in the United States per year compared with the duration that would occur if all of the isolates were susceptible. Antimicrobial resistance also could account for an extra 8677 days of hospitalization for nontyphoidal salmonellosis, mainly arising from food animals.