In April 2018, a 69-year-old man with a history of DM and chronic kidney disease and undergoing dialysis treatment was admitted to Okinawa Miyako Hospital after complaints of slight bloody sputum for the past seven days and weight loss of 5 kg in the past six months.
On admission, he was afebrile and did not present with respiratory distress; vital signs were normal. Auscultation revealed clear respiratory sounds, and other physical examinations also yielded unremarkable findings. However, blood tests revealed elevated white blood cell count (12,700 cells/microL) and C-reactive protein levels (14.76 mg/dL). A computed tomography (CT) scan of the chest showed multiple consolidations with cavities in both lung fields (Figure 1). The patient had routine chest X-rays every three months, due to ongoing dialysis treatment, to check his cardio-thoracic ratio and the chest radiographs from one, four, and six months ago also showed multiple interstitial infiltrations. The locations of these infiltrations were consistent with the lung abscesses revealed by the CT on admission; these results indicated that the abscesses had existed for at least six months (Figure 1). He was hospitalized based on the diagnosis of multiple lung abscesses. Additional examinations such as urine culture, cardiac ultrasonography, and CT scans of the abdomen and head were performed to determine whether this patient had other primary source or metastatic infections. Other sources of primary and metastatic infections, such as infective endocarditis, liver abscess, brain abscess, or ocular infection, were all absent.
To determine the causative pathogen, we performed a bronchoscopy. Gram-stain of bronchoalveolar lavage fluid (BAL) showed only capsulated gram-negative rods (Figure 2), and the microorganism was identified as K. pneumoniae by conventional methods. The involvement of other pathogens, such as anaerobes, was not evident from the BAL cultures. Two sets of blood cultures were also negative for other microorganisms. String test of the isolate was positive (the string reached a length of 12 mm), which is characteristic of the hypermucoviscous phenotype. The isolate was susceptible to all routinely tested antibiotics except ampicillin. We initially treated the patient with ampicillin/sulbactam for three weeks. Next, he received oral amoxicillin/clavulanic acid suppression therapy for four weeks, after which he recovered without recurrence.
We performed multiplex PCR (Figure 3) and multilocus sequence typing as described previously. We determined the capsular serotype of the isolate to be K2 and ST 375: K2-ST375; the isolate possessed rmpA (a positive regulator of capsular polysaccharide production), iutA, entB, and mrkD. The isolated strain produced a positive string test and a positive PCR amplification of the rmpA gene; therefore, we identified the isolated strain as hypervirulent.