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

Figures & data

Table 1 Monthly number of patients positive for Staphylococcus aureus, those positive for methicillin-resistant S. aureus (MRSA), and inpatients having been positive for MRSA as outpatients (Outpt+)

Location	Major disciplines	No of Outpt+/MRSA/S. aureus	Ratio of Outpt+/MRSA	Ratio of MRSA/S. aureus	Beds
Outpatient units		NA/631/1,807	NA	0.349
Wards
Pediatrics	Pediatrics	33/56/161	0.589	0.348	26
3A	Cardiovascular medicine-surgery	76/234/377	0.325	0.621	52
3B	Obstetrics/gynecology	0/4/10	0.000	0.400	20
4A	Neurosurgery	14/228/301	0.061	0.757	51
4B	Orthopedics	101/200/325	0.505	0.615	53
5A	Surgery	29/209/282	0.139	0.456	52
5B	Surgery/orthopedics	38/122/205	0.311	0.595	54
6A	Respiratory care	96/288/366	0.333	0.787	49
6B	Hematology/radiology	15/70/124	0.214	0.565	54
ICU	Intensive care unit	31/190/287	0.163	0.662	8
Wards subtotal		433/1,601/2,438	0.270	0.657	419
Total		NA/2,232/4,245	NA	0.526

Note: Numbers are permitted for monthly repetition.

Abbreviations: MRSA, methicillin-resistant S. aureus; NA, not applicable; Outpt+, outpatients.

Figure 1 Annual patient ratios of methicillin-resistant Staphylococcus aureus to S. aureus in outpatients ≤ 15 years old, in outpatients > 15 years old, and in inpatients. For reference, the ratios of specimens derived from the lower respiratory tract are depicted. Lower respiratory tract and inpatient ratios show decreasing trends.

Abbreviations: Inpt, inpatient; LRT, lower respiratory tract; Outpt, outpatient; yo, years old.

Table 2 Minimum inhibitory concentration of 50 percentile (MIC50) and of 90 percentile (MIC90) of methicillin-sensitive and -resistant Staphylococcus aureus (n = 2,438) isolated from inpatients

Drugs	2006/01–2008/06	2008/07–2010/12
	Mina/MIC50/ MIC90/maxb (n = 1,233)	Min/MIC50/MIC90/max (n = 1,205)
Arbekacin	0.5/0.5/1/16	1/1/1/8
Ampicillin-sulbactam	1/12/32/48	1/8/32/32
Cefazolin	1/32/32/32	1/32/32/64
Cefmetazole	4/16/64/64	4/16/64/64
Clindamycin	0.25/4/4/4	0.25/4/8/8
Fosfomycin	4/4/32/32	4/8/32/128
Gentamicin	0.5/8/16/16	0.5/4/16/16
Imipenemc	1/4/16/16	1/2/16/16
Levofoxacin	0.25/4/8/8	0.12/4/8/8
Methicillin	0.25/4/4/4	0.25/4/4/4
Minocycline	0.5/0.5/16/16	0.5/0.5/16/16
Teichoplanin	1/1/2/4	0.5/1/1/8
Vancomycin	1/1/1/2	0.5/1/2/4

Notes:

a Minimum MIC;

b maximum MIC;

c without cilastatin by definition.

Abbreviations: max, maximum; MIC, minimum inhibitory concentration; min, minimum.

Figure 2 Annual trend of AUD in 22 agents. AUDs of ampicillin-sulbactam and cefazolin are high, but over time, like other agents, their AUDs fuctuate.

Note: Vertical axis shows the median values of AUDs.

Abbreviation: AUD, antimicrobial use density.

Figure 3 AUD of four agents by ten wards over 60 months (n = 600). AUDs of meropenem and ampicillin-sulbactam (Ampicillin-s) are highest in the respiratory care ward (Respir) whereas AUD of imipenem-cilastatin (Imipenem-c) is highest in the surgery ward.

Note: Vertical axis shows median values of AUDs.

Abbreviations: AUD, antimicrobial use density; CVS, cardiovascular service; Ortho1, 1st orthopedics; Ortho 2, 2nd orthopedics; ICU, intensive care unit; OBG, obstetrics and gynecology; Respir, respiratory care ward.

Table 3 Questionnaires (n = 1,016) for (A) infectious status and (B) propagation route discerned by physicians in charge of patients positive for MRSA

	2006/01–2008/06	2008/07–2010/12	Total
(A) Infectious status
Overt infection
Not related to MRSA	125 (59.2%)	86 (40.8%)	211 (100.0%)
Related to MRSA	179 (52.5%)	162 (47.5%)	341 (100.0%)
Colonization	128 (56.4%)	99 (43.6%)	227 (100.0%)
Undetermined	82 (52.6%)	74 (47.4%)	156 (100.0%)
No responsea	50 (61.7%)	31 (38.3%)	81 (100.0%)
Total	564 (55.5%)	452 (44.5%)	1,016 (100.0%)
(B) Propagation route
Imported from elsewhere	260 (51.1%)	249 (48.9%)	509 (100.0%)
In hospital	56 (60.2%)	37 (39.8%)	93 (100.0%)
Undetermined	165 (55.5%)	132 (44.5%)	297 (100.0%)
No responseb	83 (70.9%)	34 (29.1%)	117 (100.0%)
Total	564 (55.5%)	452 (44.5%)	1,016 (100.0%)

Notes: When a patient was once found positive for MRSA, the physicians judged whether the patient was colonized with MRSA or manifesting infection by the physical status and the clinical workup of the patient.

a,b Excluding no responses, Pearson’s Chi-square tests do not show significance (^aP = 0.40; ^bP = 0.18) in both series.

Abbreviation: MRSA, methicillin-resistant Staphylococcus aureus.

Figure 4 (A) Univariate and (B) multivariate logistic regression analysis on the ward-specific antimicrobial use density (ampicillin through tobramycin) and other factors for the patient ratios of methicillin-resistant Staphylococcus aureus (MRSA)/S. aureus.

Notes: Diamonds indicate odds ratio; horizontal bar represents 95% confidence interval; *statistical significance (P < 0.05); **not available due to sample deviation.

Abbreviations: LRT, lower respiratory tract; MRSA, methicillin-resistant Staphylococcus aureus.