A 37-year-old homeless patient was admitted after being found lying in the street, weak but fully conscious. On arrival, the patient did not have any localizing symptoms but admitted to using intravenous (IV) heroin the same evening. One month prior to his current admission, he was observed for a small abscess in his right arm for which he refused percutaneous draining. The patient's previous medical history includes untreated schizophrenia and glucose-6-phosphate dehydrogenase deficiency. During his current presentation, his vital signs were within normal limits and his physical examination was unremarkable except for a small abscess in his right arm. His blood tests were significant for a slightly elevated white blood cell count of 12.3*10^9/L with a relative neutrophilia of 83.5%, hemoglobin 11.1 gr%, sodium 125 mmol/L and an elevated CRP of 13.7 mg/dl. The rest of his blood tests, including ethanol, were normal. Urine toxicology was positive for cannabinoids and morphine. His chest X-ray was unremarkable, and electrocardiogram showed sinus tachycardia with no other abnormalities. On further exam, this finding on his right arm was determined to be an area of induration and cellulitis with no abscess. Early after his admission, he started suffering from a high fever, up to 40°C. Blood cultures were obtained and antibiotic treatment with IV cefazolin 1,000 mg tid was initiated. Concurrently, a new systolic murmur in the left sternal border was noted. His blood cultures were positive for methicillin-resistant Staphylococcus aureus (MRSA) with resistances profile that included clindamycin, erythromycin and methicillin. Treatment was changed accordingly to IV vancomycin 1000 mg bid. The following day, another blood culture also came back positive for MRSA but with a difference in the resistances profile which now included chloramphenicol and methicillin. After two days, an additional blood culture came positive, but this time with methicillin-sensitive Staphylococcus aureus (MSSA), with resistances to clindamycin and erythromycin.
This raised the question of a possible lab misinterpretation or a rare case of infection with two distinct Staphylococcus aureus (S. aureus) clones simultaneously. The lab was notified of the two possibilities and to our surprise, microbiological lab analysis revealed two distinct S. aureus isolates (Fig. 1). Further analysis at the S. aureus national reference center confirmed the presence of mecA in the MRSA isolate. In addition, the isolate was Panton-Valentine Leukocidin (pvl) positive, spa type t121 (repeat succession 11-19-21-17-34-24-34-22-25), and SCCmec type IV. The MSSA isolate was found to be mecA and pvl negative, and spa type t6605 (repeat succession 08-16-02-25-02-02-25-34-25).
Due to multiple positive blood cultures with both MSSA and MRSA, a new murmur, and a history of IV drug use, endocarditis was suspected. Rheumatoid factor and complement levels were within normal limits. Trans-thoracic echocardiography showed an echogenic mass of 10x7 mm on the tricuspid valve, attached to the septal leaflet, with at least moderate tricuspid regurgitation. Trans-esophageal echocardiography confirmed the previous findings and showed flail prolapse of the septal leaflet with a ruptured chordae tendineae and a severe, very eccentric jet of tricuspid regurgitation. A diagnosis of right-sided endocarditis was confirmed.
After the initiation of vancomycin antibiotic therapy, the MRSA stopped growing from the blood cultures within two days, while MSSA cultures were still positive for additional three more days. The subsequent blood cultures were negative. The patient completed one month of treatment with IV vancomycin. He continued treatment with trimethoprim-sulfamethoxazole 800/160 mg bid and ciprofloxacin 500 mg bid orally for another week and was discharged in general good health. The patient returned to the emergency department six and seven months after discharge for various non-cardiac and non-infectious complaints. Three sets of blood cultures that were obtained on those presentations were sterile.