Burdens of Invasive Methicillin-Susceptible and Methicillin-Resistant Staphylococcus Aureus Disease, Minnesota, USA

Mackenzie Koeck; Kathryn Como-Sabetti; Dave Boxrud; Ginette Dobbins; Anita Glennen; Melissa Anacker; Selina Jawahir; Isaac See; Ruth Lynfield

Disclosures

Emerging Infectious Diseases. 2019;25(1):171-174.

Abstract and Introduction

Abstract

During August 1, 2014–July 31, 2015, in 2 counties in Minnesota, USA, incidence of invasive methicillin-susceptible Staphylococcus aureus (MSSA) (27.1 cases/100,000 persons) was twice that of invasive methicillin-resistant S. aureus (13.1 cases/100,000 persons). MSSA isolates were more genetically diverse and susceptible to more antimicrobial drugs than methicillin-resistant S. aureus isolates.

Introduction

Methicillin-resistant Staphylococcus aureus (MRSA) infections were first reported in the 1960s in healthcare facilities.^[1] Risk factors included recent hospitalization, surgery, dialysis, having a central venous catheter or other invasive medical device, chronic wounds, residence in long-term care facilities or prisons, injection drug use, and exposure to antimicrobial drugs.^[2] In the 1990s, MRSA infections caused by genetically distinct strains were observed among healthy persons in the community.^[3]

Although S. aureus has long been recognized as a major human pathogen, epidemiologic studies and infection prevention precautions in recent decades have largely focused on MRSA. We compared epidemiologic, microbiologic, and molecular characteristics of invasive methicillin-susceptible S. aureus(MSSA) infections with those of invasive MRSA infections.

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Abstract and Introduction
The Study
Conclusions
References

Table 1. Epidemiologic characteristics and concurrent conditions for patients with cases of invasive MSSA and MRSA, Minnesota, USA, August 1, 2014–July 31, 2015*
Characteristic	Total, n = 701			HO, n = 65			HACO, n = 416			CA, n = 220
Characteristic	MSSA	MRSA	p value	MSSA	MRSA	p value	MSSA	MRSA	p value	MSSA	MRSA	p value
Total	473 (67)	228 (33)	NA	40 (8)	25 (11)	0.28	260 (55)	156 (68)	<0.001	173 (37)	47 (21)	<0.01
Demographic
Median age, y	59 (0–102)	62 (0–95)	0.05	61 (0–94)	61 (17–93)	0.99	62 (0–102)	65 (5–95)	0.21	55 (0–90)	50 (0–91)	0.40
Sex
F	175 (37)	92 (40)	0.39	15 (38)	6 (24)	0.26	108 (42)	66 (42)	0.88	52 (30)	20 (43)	0.11
M	316 (67)	153 (67)	0.94	26 (65)	13 (52)	0.30	169 (65)	109 (70)	0.31	121 (70)	31 (66)	0.60
Private residence 4 d before culture	376 (79)	146 (64)	<0.01	NA	NA	NA	211 (81)	100 (64)	<0.01	165 (95)	46 (98)	0.69
LTCF past year	53 (11)	70 (31)	<0.01	4 (10)	8 (32)	0.05	49 (19)	62 (40)	<0.01	NA	NA	NA
CVC 2 d before culture	29 (6)	19 (8)	0.28	6 (15)	5 (20)	0.74	23 (9)	14 (9)	0.97	NA	NA	NA
Length of stay, d	7 (0–121)	8 (0–58)	0.05	15 (3–121)	15 (4–48)	0.91	6 (0–43)	7 (1–39)	0.11	7 (0–53)	9 (0–58)	0.15
Inpatient death	47 (10)	26 (11)	0.55	8 (20)	2 (8)	0.29	29 (11)	23 (15)	0.28	10 (6)	1 (2)	0.46
Concurrent condition
None	96 (20)	27 (12)	<0.01	1 (4)	5 (13)	0.39	14 (9)	35 (12)	0.17	12 (26)	56 (12)	0.37
Kidney disease	95 (20)	67 (29)	<0.01	9 (23)	9 (36)	0.24	77 (30)	54 (35)	0.29	9 (5)	4 (9)	0.48
Chronic skin breakdown	22 (5)	25 (11)	<0.01	<0.01	3 (12)	0.69	14 (5)	21 (13)	<0.01	5 (3)	1 (2)	1.00
D/PU	9 (2)	17 (7)	<0.01	0 (0)	0 (0)	NA	6 (2)	17 (11)	<0.01	3 (2)	0 (0)	1.00
CVD	58 (12)	46 (20)	<0.01	5 (13)	6 (24)	0.31	44 (17)	39 (25)	0.05	9 (5)	1 (2)	0.69
H/P	15 (3)	23 (10)	<0.01	1 (3)	2 (8)	0.55	9 (3)	20 (13)	<0.01	5 (3)	1 (2)	1.00
Other drug use†	41 (9)	25 (11)	0.33	4 (10)	2 (8)	1.00	21 (8)	11 (7)	0.70	16 (9)	12 (26)	<0.01
PVD	24 (5)	22 (10)	0.02	3 (8)	4 (16)	0.42	16 (6)	17 (11)	0.08	5 (3)	1 (2)	1.00
COPD	50 (11)	34 (15)	0.10	6 (15)	6 (24)	0.36	30 (12)	23 (15)	0.34	14 (8)	5 (11)	0.57
Current smoker	71 (15)	32 (14)	0.73	7 (18)	4 (16)	1.00	36 (14)	19 (12)	0.63	28 (16)	9 (19)	0.63
Diabetes	153 (32)	80 (35)	0.47	12 (30)	11 (44)	0.25	96 (37)	59 (38)	0.86	45 (26)	10 (21)	0.51
Injection drug use	25 (5)	12 (5)	0.99	0 (0)	0 (0)	NA	10 (4)	4 (3)	0.48	15 (9)	8 (17)	0.11
Obesity	70 (15)	43 (19)	0.17	8 (20)	7 (28)	0.46	47 (18)	29 (19)	0.90	15 (9)	7 (15)	0.27
Syndrome
Bacteremia	328 (69)	178 (78)	0.03	30 (75)	16 (64)	0.34	181 (70)	125 (80)	0.03	117 (68)	37 (79)	0.14
Internal abscess	25 (5)	11 (5)	0.78	2 (5)	0 (0)	0.52	16 (6)	5 (3)	0.18	7 (4)	6 (13)	0.04
Pneumonia‡	39 (8)	40 (18)	<0.01	2 (5)	8 (32)	<0.01	21 (8)	22 (14)	0.06	16 (9)	10 (21)	0.02
Septic arthritis	137 (29)	35 (15)	<0.01	3 (8)	2 (8)	1.00	67 (26)	24 (15)	0.01	67 (39)	9 (19)	0.01
Skin abscess	7 (1)	4 (2)	0.76	0 (0)	1 (4)	0.39	7 (3)	0 (0)	0.05	0 (0)	3 (6)	<0.01
Bursitis	35 (7)	10 (4)	0.12	0 (0)	1 (4)	0.39	7 (3)	3 (2)	0.75	28 (16)	6 (13)	0.57
Cellulitis	73 (15)	32 (14)	0.60	6 (15)	3 (12)	1.00	38 (15)	18 (11)	0.35	29 (17)	11 (23)	0.30
Endocarditis	23 (5)	9 (4)	0.57	2 (5)	1 (4)	1.00	12 (5)	5 (3)	0.47	9 (5)	3 (6)	0.72
Osteomyelitis	51 (11)	28 (12)	0.58	1 (3)	4 (16)	0.07	38 (15)	20 (13)	0.58	12 (7)	3 (7)	0.75
Septic shock	41 (9)	19 (8)	0.86	3 (8)	4 (16)	0.42	27 (10)	11 (7)	0.24	11 (6)	4 (9)	0.53

*Values are no. (%), median (range), or no. (range). Nonsignificant (p>0.05) differences were observed for chronic pulmonary disease, current smoker, diabetes, intravenous drug use, obesity, bursitis, cellulitis, endocarditis, osteomyelitis, and septic shock among patients with MSSA and MRSA cases and within epidemiologic classifications of MSSA and MRSA cases. CA, community associated; COPD, chronic pulmonary disease; CVC, central venous catheter; CVD, cardiovascular disease; D/PU, decubitus/pressure ulcer; HACO, healthcare-associated, community onset; HO, hospital onset; H/P, hemiplagia/paraplegia; LTCF, long-term care facility; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible S. aureus; NA, not available; PVD, peripheral vascular disease.
†Drug use other than intravenous drug use.
‡All patients with pneumonia had positive blood cultures to meet the case definition.

Table 2. Clonal groups and antimicrobial drug susceptibilities of invasive MSSA and MRSA isolates, Minnesota, USA, August 1, 2014–January 31, 2015*
Characteristic	MSSA, no. (%), n = 190	MRSA, no. (%), n = 119	p value
Clonal group
USA100	13 (7)	42 (35)	<0.01
USA200	26 (14)	0 (0)	<0.01
USA300	5 (3)	36 (30)	<0.01
USA400	1 (1)	3 (3)	0.16
USA500	2 (1)	0 (0)	0.56
USA600	13 (7)	0 (0)	<0.01
USA700	5 (3)	3 (3)	1.00
USA900	10 (5)	0 (0)	<0.01
USA1000	6 (3)	0 (0)	0.09
USA1200	2 (1)	0 (0)	0.56
Untypeable	2 (1)	0 (0)	0.56
No USA group	105 (55)	35 (29)	<0.01
Antimicrobial drug†
Clindamycin‡	176 (93)	61 (51)	<0.01
Ceftaroline	190 (100)	117 (98)	0.15
Doxycycline	185 (97)	118 (99)	0.41
Erythromycin	143 (75)	18 (15)	<0.01
Gentamicin	189 (99)	118 (99)	1.00
Levofloxacin	175 (92)	35 (29)	<0.01
Penicillin	63 (33)	0 (0)	<0.01
Rifampin	189 (99)	118 (99)	1.00
Tetracycline	177 (93)	118 (99)	0.01
Trimethoprim/sulfamethoxazole	188 (99)	119 (100)	0.53

*MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible S. aureus.
†Proportions represent isolates susceptible to an antimicrobial drug. All isolates were susceptible to daptomycin, linezolid, telavancin, and vancomycin. A total of invasive MSSA and MRSA isolates had vancomycin MICs <0.05; 86% of invasive MSSA isolates and 81% of invasive MSSA isolates had vancomycin MICs = 1; 13% of invasive MSSA isolates and 18% of invasive MRSA isolates had vancomycin MICs = 2.
‡Isolates with inducible clindamycin resistance were classified as nonsusceptible.

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Burdens of Invasive Methicillin-Susceptible and Methicillin-Resistant Staphylococcus Aureus Disease, Minnesota, USA

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