Virulent Klebsiella Pneumoniae

Special Report

By Dean L. Winslow, MD, FACP, FIDSA, Chief, Division of AIDS Medicine, Santa Clara Valley Medical Center; Clinical Professor of Medicine, Stanford University School of Medicine, Section Editor, HIV, is Associate Editor for Infectious Disease Alert.

Dr. Winslow serves as a consultant to Siemens Diagnostics and is on the Speakers Bureaus of Boehringer-Ingelheim and GSK.

Synopsis: An increasing incidence of Klebsiella pneumoniae pyogenic liver abscess complicated by endophthalmitis or central nervous system (CNS) infections has been noted over the last 20 years. This retrospective cohort study demonstrated that genotype K1 was the only significant risk factor for these complications and was independent of underlying disease in the host.

Source: Fang CT, et al. Klebsiella pneumoniae genotype K1: An emerging pathogen that causes septic ocular or central nervous system complications from pyogenic liver abscess. Clin Infect Dis 2007; 45: 284-293.

I had practiced clinical infectious diseases for many years before starting work fulltime as an attending physician at our county hospital here in San Jose. Here we serve an extremely diverse population of patients, many of whom are immigrants from Latin America, Asia (especially Southeast Asia), and sub-Saharan Africa. During the 4 years I have worked at Santa Clara Valley Medical Center, I have seen more cases of tuberculosis than in my previous 26 years combined. In addition, it seemed like I saw at least one or 2 cases of primary pyogenic liver abscess due to Klebsiella during my frequent monthly rotations on the consult service. All of these cases occurred in patients from China or other countries in Southeast Asia. Several of these patients had widely disseminated pyogenic complications including 2 with endophthalmitis.

This paper presents case summaries of 23 well-studied patients from Taiwan who presented with pyogenic liver abscess due to K. pneumoniae and either endophthalmitis, meningitis, or brain abscess, which were culled from a larger group of 177 patients with K. pneumoniae pyogenic liver abscess. Genotyping of the isolates was accomplished by sequencing of the cps gene cluster. Serum resistance was assessed with standard methods.

Key findings from this study included the striking association of genotype K1 with both primary liver abscess (81% of cases vs 42% in secondary liver abscess) and septic ocular or CNS complications (occurred in 19 % of K1 liver abscess vs 5% non-K1 associated liver abscesses). Underlying biliary tract disease, previous abdominal surgery, diabetes, and malignancy were statistically more likely in patients with non-K1 associated liver abscess. High serum resistance of K1 strains (possibly related to K1 capsular polysaccharide structure) was noted and is likely to be the major pathogen-specific virulence factor. These data demonstrate that K2 strains had reduced serum resistance compared to K1 strains, in contrast to previously published data that had suggested similar serum resistance and in vitro resistance to phagocytosis.

This study clearly shows that K. pneumoniae genotype K1 is an important emerging pathogen capable of causing widely metastatic septic disease including endophthalmitis and CNS complications.