Virulence+Prevalence+Resistance=CAMRSA

Bacterial resistance is a major public health problem that threatens many of the advances that have been made in the last century in the ongoing and interminable war between humans and microbes. S. Aureus is a common and virulent bacterium that has repeatedly shown an ability to develop resistance to antibiotics and to cause fatal epidemics. It has recently become apparent that community acquired methicillin resistant S. Aureus (CAMRSA) is on the rise. The biggest threat from infectious disease occurs when virulence, resistance and prevalence are all features of the same microbe. CAMRSA threatens to be such an organism.

Panton-Valentine leukocidin (PVL)-secreting S. Aureus is a particularly virulent strain of S. Aureus that may cause life-threatening hemoptysis, pulmonary necrosis and septic shock.The pneumonia is often preceded by influenza-like symptoms and has a high lethality rate. Lancet Leukocidin/neutrophil interactions in the pulmonary vasculature specifically may cause severe hemoptysis. S. Aureus should be considered in the differential diagnosis when adults present from the community with massive hemoptysis and suspected pneumonia. ICM Airway bleeding, erythroderma, and leukopenia are associated with fatal outcome from PVL-positive S. aureus necrotizing pneumonia. CID It is concerning that there is a rise in PVL-positive CAMRSA that may be occurring through horizontal gene transfer.CMI JID

From 2001 through 2002, there were 1647 cases of CAMRSA infection reported in Baltimore, Atlanta and Minnesota communities, representing between eight and twenty percent of all MRSA isolates. NEJM CAMRSA resulted in a range of infections such as invasive infections, including bacteremia and osteomyelitis, skin and wound infections, and pneumonia. NEJM The pneumonia severity index is a useful tool for aiding clinical judgment, guiding appropriate management and for suggesting prognosis. PSICALC, AFP

Using the best evidence, address the questions relating to the following patient:

A 53-year-old man with chronic liver disease probably secondary to a strong ethanol history is brought in by his wife from home in Baltimore with confusion, hypotension (BP = 85/50), fever (Temperature = 38.3), tachypnea (RR = 35/min) and hemoptysis. On examination, the patient is distressed and diaphoretic, he is using accessory muscles of respiration, and his pulse is thready at a rate of 110/minute. There are crackles with bronchial breath sounds heard at the right lower zone. The hematocrit = 36%, white blood count is elevated (19,000), electrolytes are within normal limits, BUN is elevated (32 mg/dL), and the arterial blood gas off oxygens reveals pH=7.32, PO2=68 mmHg, PCO2=32 mmHg. The chest x-ray shows features consistent with a right middle and lower lobe pneumonia. (See Above and URL)

The ECG shows a sinus tachycardia, but is otherwise unremarkable. The patient is becoming more lethargic and the ICU team decides to proceed with tracheal intubation, to institute mechanical ventilation and to obtain bronchial washings. Sputum is thick and bloody. Specimens from the right lower and middle lobes are sent to the laboratory. On Gram-stain, Gram-positive organisms in clusters are seen. 

Questions:

1) What is the differential diagnosis? 

2) What further tests would you request?

3) What treatment would you initiate?

4) How would you ventilate this patient? 

5) If the culture grows methicillin resistant S. Aureus (MRSA), what strains are likely in this context?

6) How, if at all, would you modify your treatment in the light of this new information?

7) What would you tell the wife about the patient's prognosis?

8) What are the treatment prospects for MRSA?