April 8th, Wednesday - Gram positives in the blood, and MRSA bacteremia

On Wednesday we discussed about what to do with a gram positive blood culture. First looking back to see why it was ordered (septic patient? fever NYD?), then assessing the patient - are they unwell? do they have a reason to have bacteria in their blood?

Above is a chart you can get by a simple google measurement. Not a bad idea to take a moment to memorize this.

Some pearls I mentioned in class - Strep bovis is associated with colon cancer and endocarditis, important to do colonoscopy and consider echo.

For trivia... Clostridium septicum is also associated with colon cancer! (wouldn't that make a great trivia question). 

So when we get gram positive cocci, we get scared! (and should). Our big question is:

Is this staph epidi, most common cantaminant of skin, often referred to as coagulase negative staph or for cool people, CON staph. Or, is this staph aureus - which is scary. If ever in any doubt, reculture the patient and give a dose of vanco which would cover both. 

When you have established staph aureus bactremia, you must think about 3 points

1. The source

2. End organ involvement - did it end up on the heart, lungs, skin, bone, brain (stroke) etc. as it has a bad reputation for that!

below is a summary from a great article defining complicated vs uncomplicated that an ID fellow I worked with summarized.

http://archinte.jamanetwork.com/article.aspx?articleid=216060

Staphylococcus Aureus (gram positive cocci in clusters) is a commensal organism that colonizes the nasopharynx, axilla, groin/perineum.

It is responsible for about 20% of bacteremia (2nd most common cause of bacteremia after coagulase-negative staph or CNST)

Staph Aureus Bacteremia can be subdivided into:

1.  Community Acquired (28%)

2.  Health Care Acquired (35%)

3.  Health-Care Associated (37%) - this is people in the community but with frequent contact with health care environments

eg. IV therapy at home, wound care, specialized nursing care, indwelling lines

      residence in nursing home or long-term care

         hospitalization for more than 2 days within the last 90 days

      dialysis or IV therapy within the last 30 days

MRSA is responsible for a minority of community acquired bacteremia (<15%) but for a larger portion of hospital acquired/associated 

20% of patients with SAB will have metastatic/deep focus of infection and the mortality rate is 20-30% even with treatment which is why you ALWAYS take staph aureus in the blood very seriously.

CA-SAB (community acquired bacteremia) is important because it implies prolonged bacteremia by the time the patient presents to hospital, making them at higher risk of complicated/metastatic infection

About 40% of patients with CA-SAB will have deep focus of infection

Complications:

1.  Infective Endocarditis:

About 25% of those with SAB will have echocardiographic evidence of IE on TEE (vs. about 7% on TTE)

Therefore, TEE is superior at detecting  IE and is usually indicated

A patient must meet certain clinical criteria in order to avoid a TEE

EVERYONE GETS A TTE  - in rare situations some ID staff may opt to not get one, but for your exams... order it.

Complication rates of staph aureus endocarditis are higher than other organisms that cause IE

When is a TTE adequate:

a. if there is an identifiable source (i.e. a line) and it is removed

b. the SAB is NOT community acquired (this does not included health-care associated)

c. bacteremia resolves in 72 hours with treatment

d. patient afebrile after 72 hours treatment

2.  Prosthetic Device Complications:

Seeding if implanted hardware including pacemakers, prosthetic joints

High predictor of relapse

Hardware should be removed if possible

3. Metastatic Seeding:

Vertebral Osteomyelitis

Septic Arthritis

Splenic Abscess

CNS (although s. aureus meningitis is not common - usually in setting of recent neurosurgery)

Pulmonary Infection (necrotizing pneumonia)

Necrotizing Fasciitis

Bacteriuria - *****anyone with staph aureus in their urine needs a blood culture done if they don't have a foley to rule out bacteremia as a source!!!!

Prognosis:

Mortality rate of untreated is >80%; treated is 20-30%

Treatment:

Empiric regimens should include possibility of MSSA and MRSA

Vancomycin is the typical empiric antibiotic;  however, you should know that vancomycin is inferior to cloxacillin and cefazolin for the treatment of MSSA so coverage should be changed as soon as MSSA is confirmed

Treatment Duration:

For the most part is at least 4-6 weeks of IV antibiotics

Two weeks are adequate ONLY if the following criteria are met:

1.  removable focus - that is removed!! (and no prosthetic material)

2.  no evidence of metastatic infection

3.  resolution of fever by 72 hours after treatment

4.  negative blood culture after 2-4 days of treatment

What about aminoglycosides as brought up by Dr. Chande? Current recommendations are not to use this routinely as when compared with beta lactam therapy, outcomes were the same except for worsening kidneys (although patients did clear their bacteremia more quickly)