Association between ward-specific antimicrobial use density and methicillin-resistant Staphylococcu aureus surveillance: a 60-month study

Abstract

It is not known whether or not ward-specific antimicrobial use density (AUD) affects the ratio of methicillin-resistant Staphylococcus aureus (MRSA) in culture-positive S. aureus. A 60-month study was attempted to ascertain the association between inpatient MRSA ratio and ward-specific AUDs as well as the former and latter study intervals, specimen types, and ward specialty. During the study, the professionals in infection control regulated the use of broad-spectrum antimicrobials and those for MRSA. By both month and ward, the ratio of inpatients positive for MRSA to those positive for S. aureus was calculated. Factors associated with MRSA ratio included AUDs averaged for the sampling month and its previous month, outpatient MRSA ratio by age, ward specialty, specimen type, and half intervals to represent historical changes. Of a total of 4,245 strains of S. aureus isolated during the 5-year study, 2,232 strains (52.6%) were MRSA. By year, outpatient MRSA ratio at age ≥15 decreased in later years, as did inpatient MRSA ratio. Multivariate analysis for inpatient MRSA ratio revealed a positive risk in AUDs for meropenem (odds ratio [OR] 1.761; 95% confidence interval [CI] 1.761–2.637, P = 0.01), imipenem-cilastatin (OR 1.583; 95% CI 1.087–2.306, P = 0.02), ampicillin-sulbactam (OR 1.623; 95% CI 1.114–2.365, P = 0.01), and minocycline (OR 1.680; CI 1.135–2.487, P = 0.01), respiratory care ward (OR 2.292; 95% CI 1.085–4.841, P = 0.03), and outpatient MRSA ratio (OR 1.536; 95% CI 1.070–2.206, P = 0.02). Use of broad-spectrum antimicrobials, such as meropenem, imipenem-cilastatin, and ampicillin-sulbactam may increase inpatient MRSA ratio. Ward factor should be included in MRSA surveillance because of the possible effect on AUD and considering patients’ backgrounds.

Keywords:

• surveillance
• respiratory tract
• methicillin-resistant Staphylococcus aureus

Supplementary material

Questionnaire issued to physicians in charge of patients positive for methicillin-resistant Staphylococcus aureus. A translation from the Japanese original.

A strain of MRSA was isolated from this patient. Please answer following questions.

Q1. What was the specimen positive for MRSA?

A1. Sputum/Tracheal tube/Decubitus/Drainage tube/Pus/Blood/Urine/Blood vessel catheter/Other (specify:)

Q2. When did you submit the specimen?

A2. Year: , Month: , Day:

Q3. What infectious status do you think patient was at submission?

A2. (1) Manifest infection, if so, specify: Due to MRSA/Due to MRSA and other(s)/Causality unknown either MRSA or other(s) (2) MRSA colonization

Q4. Where do you think MRSA was acquired?

A4. Imported from community/Within hospital/Unknown

Q5. Was the patient postoperative?

A5. Yes (specify operation date:)/No

Q6. What was the main diagnosis of the patient? In what ward was the patient?

A6. (specify diagnosis and ward:)

Q7. Please give comments, if any.

A7. (describe:)

Thank you for your cooperation.

Disclosure

The authors report no conflicts of interest in this work.