Patients Presenting to the Hospital With MRSA Pneumonia: Differentiating Characteristics and Outcomes With Empiric Treatment

Emi Minejima; Mimi Lou; Paul Nieberg; Annie Wong-Beringer

BMC Infect Dis. 2014;14(252)

Abstract and Introduction

Abstract

Background: Concern for MRSA in patients presented to the hospital with pneumonia may be overestimated leading to excessive prescribing of empiric anti-MRSA therapy. This study aims to identify at-risk patients and treatment outcomes.

Methods: Adults hospitalized during 2005–2011 with pneumonia diagnosed within 48 h of admission were included. Medical charts were retrospectively reviewed for relevant data. Patients with MRSA were matched 1:1 to those with non-MRSA pathogen or negative culture. A published risk scoring system for MRSA pneumonia was applied.

Results: 268 elderly patients were included, 134 patients in each group. Compared to non-MRSA group, MRSA patients presented more acutely ill (p < 0.0001) (pneumonia severity index score, 150 vs 93; vasopressor therapy, 34% vs 6%; ICU admission, 47% vs 13%; and mechanical ventilation, 35% vs 10%) and had worse outcomes (p < 0.0001) (time to reach clinical stability, 6 vs 2.5d; length of stay, 10 vs 5d; clinical failure, 28% vs 4%; 28-day mortality, 22% vs 3%). When applied to our patients, a published risk scoring scheme had 93% sensitivity but lacked specificity at 55%; 40% of medium-risk patients did not have MRSA. A history of MRSA infection or pneumonia differentiated the latter group. Most MRSA patients (66%, 88/134) were treated empirically (primarily vancomycin) but outcome was not improved by receipt of empiric therapy.

Conclusions: Use of a published risk scoring scheme with additional variables from this study can potentially reduce overprescribing of anti-MRSA empiric therapy in patients presented to the hospital with pneumonia. Prospective studies evaluating the treatment benefit of non-vancomycin alternatives as empiric therapy are needed.

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Abstract and Introduction
Background
Methods
Results
Discussion
Conclusions
References

Table 1. Demographics and patient characteristics
Characteristics	MRSA pneumonia n = 134 (%)	Non-MRSA pneumonia n = 134 (%)	p value
Demographics
Age [median (IQR)]	82 (71.5, 89)	75.5 (62, 85)	0.0002
Male	67 (50)	62 (46)	0.62
Residence prior to admission
Home	35 (26)	110 (82)	< 0.0001
SNF	98 (73)	23 (17)	< 0.0001
Other hospital	1 (0.7)	1 (0.7)	1
APACHE II [median (IQR)]	15 (11,20)	10 (7,13)	<0.0001
Comorbid conditions
Cardiovascular disease^a	92 (69)	84 (63)	0.37
Diabetes	44 (33)	26 (19)	<0.0001
Cerebrovascular accident (CVA)	41 (31)	9 (7)	<0.0001
Liver disease^b	6 (4)	4 (3)	0.74
Renal disease^c	22 (16)	8 (6)	0.011
Pulmonary disease^d	47 (35)	39 (29)	0.24
Malignancy	21 (16)	14 (10)	0.37
≥3 comorbid conditions	86 (64)	40 (30)	<0.0001
Healthcare exposure history
History of MRSA infection	27 (20)	1 (0.7)	<0.0001
History of MRSA pneumonia	14 (10)	0	<0.0001
Prior healthcare exposure (within 90 days)	120 (90)	50 (37)	<0.0001
Prior antibiotic exposure (within 90 days)	70 (52)	23 (17)	<0.0001
Days since last antibiotic given [median (IQR)]	24 (7,41)	7 (0,32)	0.629
Prior history of pneumonia within 1 year	56 (42)	16 (12)	<0.0001
Presence of feeding tube	67 (50)	15 (11)	<0.0001
Presence of feeding tube plus history of CVA	26 (19)	4 (3)	<0.0001
Clinical presentation
Presence of other infections on admission	55 (41)	13 (10)	<0.0001
Admission of intensive care units	63 (47)	18 (13)	<0.0001
Sepsis requiring vasopressor support	45 (34)	8 (6)	<0.0001
Need for mechanical ventilation	47 (35)	14 (10)	<0.0001
PSI class IV or V	123 (92)	71 (53)	<0.0001

NOTE: SNF = skilled nursing facility; PSI = Pneumonia Severity Index; APACHE = Acute Physiology and Chronic Health Evaluation; IQR = interquartile range; ^aHypertension, congestive heart failure, prior myocardial infarction, coronary artery disease; ^bTotal bilirubin >2.5 mg/dL; ^cScr >2, Chronic Kidney Disease stage 3 orworse; ^dChronic obstructive pulmonary disease, emphysema, asthma. Fisher's exact or Chi-square test done for categorical variables; p value < 0.05 denotes significance.
Wilcoxon-Mann–Whitney test done for continuous variables, p value < 0.05 denotes significance.

Table 2. Risk factors predictive of MRSA pneumonia by multivariate logistic regression
Variable	OR (95% CI)	p-value
Age	0.995 (0.970 - 1.021)	0.7119
APACHE II	1.035 (0.972 - 1.103)	0.2833
≥3 comorbid conditions	1.947 (0.975 - 3.888)	0.0588
PSI IV & V	3.827 (1.260 - 11.626)	0.0179
Residence in SNF prior to admission	5.301 (2.585 - 10.870)	<0.0001
Presence of other infections at admission	3.686 (1.515 - 8.967)	0.0040
Prior antibiotic exposure within 90 days	4.624 (2.158 - 9.909)	<0.0001
Presence of feeding tubes	2.357 (1.062 - 5.231)	0.0350

NOTE: PSI = Pneumonia Severity Index; APACHE = Acute Physiology and Chronic Health Evaluation.

Table 3. Clinical characteristics, empiric treatment, and outcomes of patients stratified by risk for MRSA
	Stratification by Shorr risk scoring scheme
	Low risk (0–1)			Medium risk (2–5)			High risk (6–10)
	MRSA n = 9 (%)	Non-MRSA n = 74 (%)	P value	MRSA n = 86 (%)	Non-MRSA n = 58 (%)	P value	MRSA n = 39 (%)	Non-MRSA n = 2 (%)	P value
Variables used in Shorr's risk scoring scheme
Age [median (IQR^a)]	66 (61,76)	74.5 (61,84.3)	0.42	84 (72.8, 89.3)	77 (63.5,85.3)	0.01	82 (76,93)	85.5 (82,89)	0.7
Recent hospitalization within 90 d	0	0		27 (31)	26 (45)	0.12	35 (90)	1 (50)	0.23
Prior antibiotic exposure in last 30 d	0	2 (3)	1	20 (23)	8 (14)	0.2	22 (56)	1 (50)	1
SNF	5 (56)	3 (4)	0.0002	63 (73)	18 (31)	<0.0001	30 (77)	2 (100)	1
Admission into ICU	0	0		34 (40)	16 (28)	0.16	29 (74)	2 (100)	1
History of CVA	0	1 (1)	1	23 (27)	8 (14)	0.1	18 (46)	1 (50)	1
Female with diabetes	1 (11)	3 (4)	0.37	15 (17)	9 (16)	0.82	9 (23)	0	0.07
Additional variables identified in this study (not included in Shorr's risk scoring scheme)
APACHE II [median (IQR)]	11 (8,18.5)	9 (7,11)	0.1	15 (11, 19.3)	12 (8,17)	0.006	18 (13,22)	21.5 (21,22)	0.52
PSI IV and V	8 (89)	31 (42)	0.01	78 (91)	38 (66)	0.0004	37 (95)	2 (100)	1
Vasopressor	0	0		25 (29)	6 (10)	0.0075	20 (51)	2 (100)	0.49
Mechanical ventilation	1 (11)	0	0.11	27 (31)	13 (22)	0.26	19 (49)	1 (50)	1
Prior antibiotic exposure in last 90 d	1 (11)	3 (4)	0.37	29 (34)	19 (33)	1	35 (90)	1 (50)	0.23
History of MRSA infection	1 (11)	1 (1)	0.2	19 (22)	0	<0.0001	7 (18)	0	1
History of pneumonia	1 (11)	5 (7)	0.5	33 (38)	10 (17)	0.009	22 (56)	1 (50)	1
Presence of other infections at admission	1 (11)	1 (1)	0.2	36 (42)	11 (19)	0.006	18 (46)	1 (50)	1
Presence of feeding tube	0	0		32 (37)	13 (22)	0.07	34 (87)	2 (100)	1
Treatment
Empiric anti-MRSA therapy	3 (33)	15 (20)	0.4	58 (67)	22 (38)	0.0006	27 (69)	1 (50)	0.54
Vancomycin	2 (67)	15 (100)	0.17	53 (62)	20 (91)	0.002	21 (54)	1 (100)	1
Other agents	1 (33)	0		5 (6)	2 (9)	0.7	6 (15)	0	1
Outcomes
Time to stability [median days (IQR)]	4 (3,11)	1 (1,4)	0.03	6 (4,10)	4 (1,7)	0.052	6.5 (5.3,12.8)	9.5 (0,19)	#
Clinical failure	1 (11)	0	0.11	23 (27)	5 (9)	0.0092	14 (36)	0	0.54
Mortality 28-day	0	0		18 (21)	4 (7)	0.03	11 (28)	0	1
LOS^b survivors [median days (IQR)]	9.5 (7,15)	4.5 (3,7)	0.0005	10 (7,14)	7 (5,14.3)	0.1	10 (6,17)	12.5 (5,20)	0.93
Readmission 30-day	2 (22)	3 (4)	0.09	10 (12)	9 (16)	0.65	6 (15)	0	1

NOTE: ^aIQR = interquartile range; ^bLOS = length of stay; CVA = cerebral vascular accident; SNF = skilled nursing facility; PSI = Pneumonia Severity Index; APACHE = Acute Physiology and Chronic Health Evaluation; # n too small.
Chi-square test done for categorical variables; p value < 0.05 denotes significance.
Wilcoxon-Mann–Whitney test done for all continuous variables; p value < 0.05 denotes significance.

Table 4. Comparison of patient characteristics and outcomes of those with MRSA pneumonia who received empiric vs directed anti-MRSA therapy
Characteristics	Empiric n = 88 (%)	Directed n = 46 (%)	p value
Age [median (IQR^a)]*	81 (72.3,88)	85.5 (69.8,93)	0.35
Residence prior to admission
Home	15 (17)	20 (43)	0.004
SNF	72 (82)	26 (57)	0.004
APACHE II score [mean, SD^b]^Y	17.9 ± 6.9	13.1 ± 5.2	<0.0001
PSI score [mean, SD]^Y	153.4 ± 36.82	131.3 ± 34.9	0.0011
Mechanical ventilation	33 (38)	14 (30)	0.45
Duration of mechanical ventilation [median IQR]*	3 (2,7)	6 (2.5,20.75)	0.064
Vasopressor use	37 (42)	8 (17)	0.0041
Outcomes
Time to reach clinical stability [median (IQR)]*	7 (4,10)	6 (3.5,11.5)	0.47
Clinical response	55 (63)	35 (76)	0.12
Mortality at 28 days	24 (27)	5 (11)	0.029
Readmission within 30 days	11 (17)	7 (18)	0.79
Length of hospital stay of survivors [median (IQR)]*	10 (6,15)	8.5 (7,14.3)	0.50

NOTE: ^aIQR = interquartile range; ^bSD = standard deviation; SNF = skilled nursing facility; PSI = Pneumonia Severity Index; APACHE = Acute Physiology and Chronic Health Evaluation.
Chi-square test done for categorical variables; p value < 0.05 denotes significance.
*Wilcoxon-Mann-Whitney test, p value < 0.05 denotes significance.
^YStudent's t-test, p value < 0.05 denotes significance.

Table 5. Risk factors predictive of 28d mortality in patients with MRSA pneumonia by multivariate logistic regression
	OR (95% CI)	p value
Receipt of empiric anti-MRSA therapy	1.634 (0.461 - 5.793)	0.4468
Renal dysfunction	2.797 (0.838 - 9.343)	0.0946
Mechanical ventilation	2.747 (0.941 - 8.024)	0.0646
Vasopressor requirement	3.602 (1.078 - 12.039)	0.0374
APACHE II score	1.087 (0.987 - 1.198)	0.0903