Antimicrobial Resistance: the importance of large problems far away versus small problems closer to home

Tjibbe Donker writes here about his BMC Medicine study, aiming to help control the spread of antimicrobial resistance between hospitals by comparing the severity and closeness of cases.

Antimicrobial resistance forms a formidable threat to the effective treatment of infections, in particular for hospitalized patients. These patients are susceptible to infections due to their medical condition or the procedures they have undergone. As antibiotics become less effective, infections that used to be benign can become life-threatening.

Hospitals are an ideal breeding ground for antibiotic-resistant bacteria, because of a combination of a patient population susceptible to bacterial infections and high antibiotic use. To protect patients from infections with resistant bacteria, hospitals actively try to avoid the introduction of antibiotic resistance into their patient population.

Avoiding introductions can, for instance, be done by screening patients who are at risk of already carrying these bacteria, such as those patients that have previously been admitted to a hospital that has a large problem with antibiotic-resistance. These patients could seed a new outbreak in their new hospital, which could be prevented if they are identified and isolated on admission. It is in that respect convenient to make a short-list of hospitals that are known to have a problem, such as large outbreaks.

Avoiding introductions can, for instance, be done by screening patients who are at risk of already carrying these bacteria.

We wanted to know if hospitals with a high prevalence of antibiotic-resistant bacteria, those that are likely to be included on a high-risk list, had the largest risk for the other hospitals in the country in relation to the number of patients these hospitals exchange.

We took the distribution of Carbapenemase-Producing Enterobacteriaceae (CPE) as an example, to study the interplay between the prevalence of resistant bacteria and the numbers of exchanged patients. CPE is a group of gram-negative bacterial species that are resistant against some of the last available antibiotics, that form an increasing problem in hospitals worldwide.

We estimated the regional prevalences of CPE, based on the number of CPE isolates received and confirmed by the reference laboratory at Public Health England. These prevalences were used, together with the patient flows between hospitals, to calculate the number of expected introductions for each hospital.

Despite a large outbreak of CPE in the North-West of England that caused a considerable difference in prevalence between regions, almost all hospitals could expect the majority of CPE introductions to come from their directly neighboring hospitals, rather than the high-risk ones.

The effect we found is caused by the large differences in the number of exchanged patients between hospitals.

The effect we found is caused by the large differences in the number of exchanged patients between hospitals; as a rule of thumb, hospitals in the same region exchange 100 times more patients with each other than with hospitals in different regions. The same prevalence in a neighboring hospital will, therefore, result in 100 times more received CPE colonized patients, compared to a hospital further away. So even if the prevalence far away is much higher, in absolute numbers most colonized patients are received from the neighboring hospitals. The number of introductions from hospitals far away only start to contribute substantially if the prevalence there is over 100 times higher.

The focus of control efforts is often drawn towards big outbreaks because they are more likely to be reported and perceived as a major threat. In the meantime, a larger threat is posed by the hospitals with fewer cases, which often go under-reported. This difference in reaction between the actual and the perceived threat may ultimately undermine all control efforts.

To effectively adjust control efforts to the actual threat of introductions from other hospitals, all hospitals need to have a complete picture of the current prevalence in each hospital, in particular, their surrounding hospitals, not just the hospitals with the biggest problems. This can, for instance, be achieved by performing point prevalence surveys, and actively sharing the results with the other hospitals.

Above all, hospitals need to actively collaborate in the coordination of infection prevention and control efforts, because their antibiotic resistance problems are connected through their shared patients.



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