This study aims to assess how large an additional disease burden and what extra costs are generated by antibiotic resistance in patients suffering from infections caused by gram-negative bacteria, such as Escherichia coli and Pseudomonas aeruginosa, in hospitals in the Netherlands.

This study addresses the following three aims:

1. To provide a more accurate estimate than currently available of the incremental disease burden and attributable costs of antibiotic-resistant as compared to antibiotic-sensitive gram-negative bacteria (i.e. Enterobacteriaceae and non-fermenters). This analysis is focused on gram-negative infections for which patients are hospitalized. In a less detailed manner, the same analysis of disease burden and costs can be performed for acquiring a gram-negative infection during hospitalization.
2. To identify determinants associated with resistance in gram-negative infections, to the extent that they are confounders of the relation between resistance and outcome.
3. To adapt and optimize existing methodology to measure the burden of resistance, among others by calculating disability-adjusted life years (DALYs) which incorporate not merely mortality, but also morbidity.

GRAND-ABC is designed as a prospective parallel matched cohort, which will run for a year in each of the eight participating hospitals. The primary cohort is a random sample of all Gram-negative infections occurring in a participating hospital during the study period. This cohort can be divided on the basis of the primary determinant status (whether the Gram-negative pathogen is resistant or not based on Dutch guideline for multi-drug resistant organisms; Werkgroep Infectiepreventie (WIP). Bijzonder resistente micro-organismen (BRMO). December 2012. http://www.wip.nl/free\_content/Richtlijnen/130424\_BRMO.pdf) into two parallel subcohorts. Each patient in each of the subcohorts will be matched to one patient without a gram-negative infection. Together these will form the secondary cohort of non-infected patients: patients admitted to the hospital during the study period who are within the same risk set as the infected patients.

For all patients data collection will be performed by review of medical files, which will cover the entire admission during which they were included in the study, and all cause 30 day mortality. Data collection for the hospital stay covers confounders and effect modifiers of the associations studied, and feeds into the outcomes costs, DALYs and length of stay. For the cohort with gram-negative infections, data on infection parameters and antibiotic treatment parameters are also collected.

In addition, the subcohort with infections by multi-drug resistant organisms and a random 20% of the subcohort with infections by sensitive organisms will be selected for follow-up, consisting of sending questionnaires and renewed medical file review 30 days after the index culture date. In the case of ongoing sequelae of the gram-negative infection, this procedure is repeated 90 days after the index culture date. These questionnaires will feed into the outcomes costs, DALYs and quality-adjusted life years (QALYs).

Inclusion Criteria:

• Please refer to descriptions of two cohorts

Exclusion Criteria:

• Patients on children's wards
• Patients admitted to wards for long-term care or psychiatric wards, that were not subsequently admitted to acute care wards as a consequence of the infection
• Patients admitted to wards that are excluded for logistic reasons such as the non-availability of electronic patient files, that were not subsequently admitted to included acute care wards as a consequence of the infection
• Patients that have been included in the cohort of infected patients during the same hospitalization or within the past 30 (if not eligible for follow-up) or 90 (if eligible for follow-up) days

Patients admitted to hospitals