Stone-related pyelonephritis can result in urinary tract infections (UTI) and is a potential risk of urosepsis. Empiric antibiotics therapy with urinary drainage is a mainstay of treatment, but the causative agents of stone-related pyelonephritis are diverse and different from those of uncomplicated UTI [1].

In recent years, as the number of elderly people has increased, there has been an increase in the number of patients with underlying disease (e.g., hypertension and diabetes mellitus), patients using steroids, patients with poor Performance status (PS), patients with a history of antibacterial drug use, and patients with a history of hospitalization. The literature on the pathogens of pneumonia reports that drug-resistant pathogens are more likely to be detected in patients with such underlying disease, in patients with a history of hospitalization and antimicrobial therapy, in immunosuppressed patients, and in patients with poor PS [2,3].

Complicated UTIs have been suggested to have a higher proportion of Gram-positive cocci (GPC) such as Enterococci, Staphylococci, and group B Streptococci, and a lower proportion of Escherichia coli (E.coli) compared with uncomplicated UTI [1,4,5]. If GPC is the organism causing the infection, a different choice of antimicrobial agent is often necessary. Cephalosporins, which are commonly used for UTI, are ineffective for Enterococci, and vancomycin is required for methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus feacium. However, most of the patients in these studies had urinary catheters, which likely greatly impacted upon the results, because the literature on catheter-associated urinary tract infections shows a higher proportion of GPC, such as enterococci [5]. The characteristics of causative bacteria in stone-related pyelonephritis have not yet been sufficiently investigated.

This study evaluates the causative organisms of stone-related pyelonephritis and compares the distribution of pathogens according to patient background, such as performance status, history of antibacterial drug use, and history of hospitalization within six months.