1. Community-Associated MRSA Infections
Roger D. Smalligan, MD, MPH
Assistant Professor of Internal Medicine and Pediatrics
Quillen College of Medicine
East Tennessee State University

2. Staphylococcus aureus

21. History of MRSA
1961 – 3 isolates of MRSA discovered among 5000 isolates in Great Britain
1980s – became common in hospitals
1990s – spread to nursing homes and communities

22. Methicillin Resistance - Mechanism
Methicillin binds to PBP (Penicillen Binding Protein - cell wall protein) and inactivates it
MRSA has PBP2a - beta-lactams cannot attach

23. Methicillin resistance – gene location
PBP2a - encoded by mecA gene
mecA - on Staphylococcal Cassette Chromosome (SCC)

24. HA & CA MRSA are genetically distinct
Hospital-associated (HA) MRSA have SCCmecA types I-III
Community-associated (CA) MRSA have SCCmecA type IV or V

25. Genetically distinct CA-MRSA HA-MRSA (SCCmecA Type II)
(SCCmecA Type IV)
HA-MRSA
(SCCmecA Type II)

26. CA-MRSA strains
USA 400 clone – initially identified in midwest – now nationwide
Pharmacotherapy Jan;25(1):74-85
USA 300 clone – identified in 99% of CA-MRSA infections in Atlanta recently
Ann Intern Med 2006;144:

27. HA-MRSA CA-MRSA SCCmecA I-III SCCmecA IV-V
Chronically ill Young, athletes, prisoners
Hospital / healthcare No healthcare contact
Previous antibiotics No previous treatment
Multi-drug resistant Usually susceptible still
IV cath/surgical wounds Skin infections / boils
Bacteremia without focus Necrotizing pneumonia

28. CA-MRSA: CDC definition
Positive MRSA culture as an outpatient or within 48 hours of admission
No previous history of MRSA
No surgery / admission / nursing home / dialysis unit in past year
No indwelling catheters or devices

29. MRSA Awareness in Sports
MRSAAwareness.com

30. CA-MRSA Risk Groups Prison inmates Injection drug users
Men who have sex with men
HIV-infected individuals
Competitive sports participants
US Army soldiers
Children attending daycare

31. CA-MRSA in the Emergency Room
August 2004 study of 11 ERs
Skin & soft tissue infection cultures
N=422; 76% Staph, 59% MRSA
(98% of these SCCmecA IV PVL positive)
Only 43% received appropriate antibiotics
NEJM 2006;355:666

32. CA-MRSA in the ER Atlanta Hospital (Grady) – over 3 months
384 skin / soft tissue infections
68% CA-MRSA
2/3 received inadequate antibiotics (initially)
Ann Intern Med 2006;144:
>50
<18
35-49
18-34
Age of patient

33. CA-MRSA in general population
10 studies (8350 people)
1.3% pooled MRSA nasal colonization rate
for community studies ( %)
0.2% MRSA prevalence among
Salgado CD, et al. Clin Infect Dis 2003;36:131-9

34. CA-MRSA in US Soldiers 812 were screened with nasal swabs
28% were colonized with S. aureus (MSSA)
3% developed skin infections
3% colonized with MRSA
38% developed skin / soft tissue infections (10 weeks)
Ellis MW, et al. Clin Infect Dis 2004;39:971-9

35. Panton-Valentine leukocidin (PVL)
Extracellular cytotoxin
leukocyte destruction
tissue necrosis
Most CA-MRSA produce this toxin

36. CA-MRSA Clinical Spectrum
77% skin and soft tissue
folliculitis
cellulitis
furuncle, carbuncle, abscess
6% invasive
pneumonia / empyema
bacteremia
septic arthritis
osteomyelitis
pyomyositis / necrotizing fasciitis

37. The “spider bite” trap

39. CA-MRSA Outpatient Treatment
I & D of small abscesses +/- antibiotics
SEND A CULTURE!
Oral antibiotic options:
- TMP/SMX
- doxycycline plus rifampin
- clindamycin (think “D-test”)
- linezolid

40. JCMC Antibiogram Vanc SXT Clinda Gent Linezo JCMC MRSA 2005 100% 94%
62%
92%
99%
JCMC MRSA 2006
75%
96%

42. JCMC MRSA Sensitivity Report
SPEC#, TYPE: NARES MICROBIOLOGY Feb 21, :48
FINAL REPORT METHICILLIN RESISTANT STAPHYLOCOCCUS AUREUS ISOLATED This {S. aureus} is presumed to be clindamycin resistant based on detection of inducible clindamycin resistance. ISOLATE 1 STAPHYLOCOC
CIPROFLOXACIN >=8 R CLINDAMYCIN <=0.25 S
ERYTHROMYCIN >=8 R GENTAMICIN <=0.5 S LEVOFLOX >=8 R LINEZOLID S OXACILLIN >=4 R
` PENICILLIN >=0.5 R RIFAMPIN <=0.5 S
SXT <=10 S TETRACYCLINE >=16 R VANCOMYCIN <=1 S

43. “Bowling Bummer” 15yo young man fell and hit knee 2 weeks prior
Sprain diagnosed in ER
Pain/swelling persisted – dx - hairline fracture
Developed fever and agitation
No history of recent infections or sick contacts

44. PMH: unremarkable
PE: ill appearing, T 101, P 138, RR 40, O2 sats 92% on 2L
CV- RRR no m/r/g Lungs- clear
Right leg – swollen/warm/tender but no overlying erythema or skin lesions

45. Labs:
WBC 50.2 with 27% bands
HCT 26
ESR 87
Blood, urine, nasal cultures grew MRSA

51. ICU Course:
Remained critical for weeks on vancomycin / gent / rifampin and eventually linezolid
Complications included:
Respiratory failure due to necrotizing pneumonia / empyema
Pyomyositis
Septic arthritis (hip, knee, elbow)
Osteomyelitis (pelvis, femur, tibia)

52. CA-MRSA Inpatient Treatment
IV antibiotics: (Consider an ID consult!)
vancomycin
linezolid
clindamycin (if susceptible)
daptomycin
tigecycline
New drugs on the horizon

53. CA-MRSA Prevention Cover all wounds with clean dressings
Wash hands frequently
Practice good hygiene
Don’t share towels, razors, combs, etc.
Clean sports equipment used by others
Get tested - mupirocin for carriers +/- polysporin for failures

54. Wilmeta will check your status if you like…