A fatal case of necrotising pneumonia due to community‐associated methicillin‐resistant Staphylococcus aureus

A 23-year-old woman presented to the emergency department with acute radicular lower back pain that became apparent when she was lifting books. She had normal blood pressure and 100% oxygen saturation breathing room air, but her heart rate was 110 beats/min and she had a temperature of 38.4° C. Inexplicably, she was discharged with a diagnosis of mechanical back pain. She presented again 2 days later with back pain, increasing shortness of breath, vomiting, myalgia, fever and sweating. She had also developed a dry cough and anterior pleuritic chest pain. There was an erythematous lesion on her left elbow. She and other family members had a history of recurrent furunculosis. When examined on admission, the patient was tachycardic (heart rate, 160 beats/min), hypotensive (blood pressure, 80/50mmHg) and hyperpnoeic (respiratory rate, 32 breaths/min), with an oxygen saturation of 100% on a non-rebreather mask with oxygen flow at 15 L/min. She was febrile, with a temperature of 38.2° C, and had a furuncle on her left elbow. She had tenderness in the right upper quadrant; the spleen was not palpable. There was midline and left paraspinal tenderness over T8/9. There was no tampon in situ. Initial investigations showed a predominantly neutrophilic leukocytosis (18.4 10 cells/L [reference range (RR), 3.5–11 10 cells/L]); coagulopathy (prothrombin time, 20 s [RR, 9–14s]; activated partial thromboplastin time, 40 s [RR, 25–38 s]); thrombocytopenia (platelet count, 59 10/L [RR, 140–400 10/L]); renal dysfunction (urea level, 14.2 mmol/L [RR, 3–8mmol/L]; creatinine level, 172 μmol/L [RR, 50–100 μmol/L]); and an elevated serum troponin I level (1.4μg/L [RR, <0.2 μg/L]). A chest x-ray showed bilateral multilobar consolidation. Initial therapy included large-volume fluid resuscitation, a noradrenaline infusion, intravenous hydrocortisone and empirical intravenous antibiotics (3.1g ticarcillin/clavulanate, 400mg gentamicin and 500mg azithromycin, within 50 minutes of arrival). Subsequently 2g dicloxacillin was administered intravenously. The patient required intubation and mechanical ventilation 6 hours after admission, due to markedly deteriorating respiratory function. At this time, arterial blood gas results measured with the patient on 100% oxygen were: pH, 7.13 (RR, 7.35–7.45); partial pressure of carbon dioxide (PaCO2), 52 mmHg (RR, 35–45mmHg); PaO2, 237 mmHg (RR, 75–100mmHg); base deficit, –12.3mmol/L (RR, –3 to 3 mmol/L); and bicarbonate, 16 mmol/L (RR, 22–33mmol/L). A computed tomography scan revealed multiple small areas of airspace opacification in a perivascular distribution, as well as bilateral extensive lower-lobe consolidation. Nine hours after admission, in view of worsening shock, drotrecogin alpha (activated protein C) and vasopressin were commenced. Despite a high-dose infusion of noradrenaline and adrenaline, the patient’s circulatory status continued to deteriorate. Staphylococcus was grown from initial blood cultures after 14 hours, and intravenous vancomycin 1000mg was administered. Sixteen hours after admission, the patient had an episode of ventricular tachycardia, which reverted to sinus rhythm after a single precordial thump. However, ventricular tachycardia recurred and progressed to asystole. The patient died 17 hours after presentation, despite resuscitation. Subsequently, methicillin-resistant S. aureus (MRSA) was grown from blood cultures, endotracheal aspirates, and furuncle swabs and biopsies. The organism was sensitive to erythromycin, clindamycin, gentamicin, tetracycline, ciprofloxacin and vancomycin. Isolates were typed using a real-time polymerase chain reaction method based on single nucleotide polymorphisms (SNP) of the core genome and the presence or absence of variable genes, including the gene for Panton–Valentine leukocidin (pvl). 1 All isolates had an SNP and variable gene profile characteristic of the Queensland clone (ST93-MRSA-IV) of community-associated MRSA (CA-MRSA), including the presence of pvl. Queensland clone CA-MRSA was also isolated from nose swabs subsequently collected from three family members, two of whom had suffered from recurrent furunculosis. Postmortem examination showed that the principal pathology lay in the lungs and myocardium. The lungs showed multiple foci of bronchopneumonia, many coalescing to form extensive areas of lobar pneumonia. However, the most striking feature seen on histology was involvement of the pulmonary vasculature by staphylococcal septicaemia. Staphylococci had invaded the walls of multiple blood vessels, producing a florid vasculitis with subsequent secondary thrombosis of the involved vessels (Figure). This process involved both large and small vessels to such an extent that a lethal degree of bilateral arterial thrombosis had developed. The larger thrombosed vessels were obvious at macroscopic examination of lung slices. Multiple small thrombi were seen on microscopy. The myocardium showed focal abscesses containing staphylococcal colonies. Adjacent myocardial fibres showed necrosis, which correlated with the patient’s raised troponin level. The other organs of the body were remarkably free of sepsis, the spleen was normal, and the spinal column showed no evidence of osteomyelitis. A furuncle on the left elbow was confirmed. ◆ Histological section of the patient’s lung at autopsy