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Table 7 Examples of study types evaluating the health impacts associated with human infections due to resistant as compared to susceptible bacterial strains

From: Antimicrobial drug use in food-producing animals and associated human health risks: what, and how strong, is the evidence?

Reference

Study

Key findings relevant to antimicrobial resistance

Typea

subjects

country

time period

bacterial target

relevant study outcomes

sample size

controls

comments

GRADE level: Controlled trial

n/a

GRADE level: observational trial

[121]

Cohort

Patients with Salmonella infections

US

1996–2001

Salmonella

Frequency of hospitalization and bloodstream infection

n = 1415 patients (FoodNet) and n = 7370 isolates (NARMS)

Patients infected with susceptible Salmonella strains

Two analyses were performed, one of Salmonella isolates collected through NARMS, and one of patients with NARMS Salmonella isolates and corresponding FoodNet interviews

Resistant isolates were more likely associated with bloodstream infections than susceptible isolates (for example, for serotype Typhimurium, 3% of patients infected with susceptible isolates had bloodstream infections, compared to 6% of patients infected with resistant strains); patients infected with resistant isolates were more likely to be hospitalized because of bloodstream infection than those infected with susceptible isolates; among hospitalized patients, those infected with resistant isolates had longer stays than those infected with susceptible isolates;

[122]

Cohort

Patients with Salmonella infections (bloodstream and GI infection)

US

2006–2008

Salmonella

Clinical outcomes

n = 875 patients

Patients infected with susceptible Salmonella strains

 

Bloodstream infections and hospitalizations more likely among patients with resistant than susceptible isolates

[123]

Cohort

Patients infected with Salmonella

US

1989–1990

Salmonella

Infection and hospitalization

 

Patients infected with susceptible Salmonella strains

Results were compared to similar study conducted in 1979–1980

Patients with resistant infections were more likely to be hospitalized than those with susceptible infections; recent antimicrobial treatment as well as age and race were significant predictors of resistance

[124]

Cohort

Patients with Salmonella infections

Canada

1999–2000

Salmonella Typhimurium

Risk of hospitalization

n = 440 patients

Patients infected with susceptible Salmonella strains

 

Hospitalization was more likely in patients infected with resistant than susceptible strains; an estimated 57–72% of hospitalizations were attributable to resistance patterns

[125]

Cohort

Patients infected with Salmonella Typhimurium

Denmark

1995–1999

Salmonella Typhimurium

Death rates

N = 2047

10 random controls (matched by age, sex and county of residence); comparison between susceptible and resistant infections

Subjects were followed for up to 2 years after entering the study

Patients with susceptible Salmonella Typhimurium infection were 2.3 times more likely to die during the study period than the general population; patients with most resistant strains were 4.8 times (95% CI: 2.2–10.2) more likely; patients infected with quinolone-resistant isolates were 10.3 times more likely to die than the general population.

[126]

Cohort

Patients with Campylobacter infections

Denmark

 

Campylobacter (quinolone and erythromycin-resistant)

Risk of invasive illness and death within up to 90 days of sample receipt

n = 3471 patients

Patients infected with susceptible Campylobacter isolates

 

Patients infected with quinolone-resistant Campylobacter strains had a 6-fold increased risk of invasive illness or death within 30 days of sample collection compared with patients infected with susceptible isolates; infection with erythromycin-resistant Campylobacter strains was associated with >5-fold higher risk within 90 days compared to infections with susceptible strains

[127]

Meta-analysis of cohort studies

Studies of patients with bloodstream infection due to Staph. aureus

multiple countries

1980–2000

Staphylococcus aureus, MRSA

Mortality rates due to infections with methicillin susceptible and resistant Staphylococcus aureus

n = 3963 patients in n = 31 studies

Patients infected with methicillin susceptible strain

Results pooled with random effects model

Increased mortality associated with MRSA infections compared to methicillin –susceptible strains (OR: 1.93; 95% CI – 1.52 – 2.42)

GRADE level: other

[128]

Outbreak analysis

Outbreaks of patients infected with Salmonella

US

1984–2002

Salmonella

Hospitalization due to infection with susceptible or resistant Salmonella strains

n = 23,206 patients in n = 32 outbreaks

Outbreaks with susceptible Salmonella strains

 

The median proportion hospitalized for each type of outbreak caused by resistant strains was 26%, 2.5 times higher than the median proportion hospitalized for outbreaks caused by pan-susceptible strains

  1. a CC case-control study (or case-case study where controls are cases of infection with other strains), CS cross-sectional study