Case Presentation: Klebsiella Pneumoniae is a gram-negative bacterium known to cause pneumonia and urinary tract infections. The hypermucoviscosity phenotype of K. pneumoniae is commonly tested for using the string test. Clinical studies have shown an association between the hypermucoviscosity phenotype and a highly virulent tissue abscess syndrome, causing liver abscesses, endophthalmitis and septic thrombophlebitis. Most of these cases have been reported in East Asian countries. We present the case of a North American patient with a string-negative K. pneumoniae infection that behaved like a hypervirulent strain.
A 55-year-old African American woman with a history of type II diabetes presented with right-sided painless vision loss. She was diagnosed with endogenous endophthalmitis by an outside ophthalomogist, and emergently transferred to our hospital for further work-up. On further questioning she endorsed several weeks of right-sided abdominal pain and one week of subjective fevers. Physical examination was notable for the absence of fever, decreased right-sided visual acuity with decreased pupillary response, and mild epigastric and right upper quadrant tenderness. Abdominal computed tomography (CT) revealed a 4.1×2.5cm collection in the hepatorenal fossa concerning for an infected perinephric phlegmon. Blood and urine cultures grew Klebsiealla pneumonia. String testing was negative.
Further work-up was performed to evaluate for metastatic spread of infection. A chest CT revealed multiple bilateral pulmonary nodules, some with cavitations, concerning for septic emboli. Transthoracic and trans-esophageal echocardiography did not show evidence of vegetations, and surveillance blood cultures remained negative. Magnetic resonance imaging (MRI) of the brain and orbit were normal.
Once microbiology data became available, her antimicrobials were narrowed from vancomycin, piperacillin-tazobactam, and voriconazole to IV cefazolin. She completed a 6-week course with significant improvement in her visual acuity.
Discussion: This case describes a woman with a K. pneumoniae urinary tract infection with secondary bacteremia and metastatic spread, including a perinephric phlegmon, septic pulmonary emboli, and endogenous endophthalmitis. Interestingly, the K. pneumoniae isolated from our patient was string-negative, suggesting that this was a less virulent strain, although it clinically behaved like a hypervirulent variant. This raises the question of whether the string test is an appropriate virulence test of K. pneumoniae.
Conclusions: Further analysis of the klebsiella genome could help clinicians determine the characteristics that pose the greatest health risks. Studies have suggested that the capsular serotype, which is another K. pneumoniae virulence factor, is a more important virulence determinant for K. pneumoniae than the hypermucoviscosity phenotype. Additionally, this infection occurred in a North American patient, when most previous reports have been from East Asia. There have been increasing reports of hypervirulent Klebsiella infections occurring in Europe and North America, and our awareness of these strains should increase.