Elsevier

The Lancet Infectious Diseases

Volume 16, Issue 9, September 2016, Pages e190-e195
The Lancet Infectious Diseases

Grand Round
Primary osteomyelitis caused by hypervirulent Klebsiella pneumoniae

https://doi.org/10.1016/S1473-3099(16)30021-4Get rights and content

Summary

Klebsiella pneumoniae is the most clinically relevant species of this genus, known to cause both community-acquired and nosocomial infections worldwide. In the past two decades, a distinct hypervirulent strain of K pneumoniae, characterised by its hypermucoviscous phenotype, has emerged as a clinically significant pathogen responsible for highly invasive infections. We present a case of osteomyelitis due to hypervirulent K pneumoniae reported in the USA. Genomic testing of the K pneumoniae isolate was performed due to the striking clinical presentation of the infection as well as the hypermucoid nature of the isolates, raising the suspicion for possible infection with the hypervirulent strain. Whole-genome sequencing and additional PCR testing demonstrated the isolate to be a K1 serotype, sequence type 23 strain expressing rmpA and rmpA2. Given the multiple reports of this pathogen causing invasive infections, clinicians should be aware of the possible presentation of metastatic and severe infection, including osteomyelitis, due to the hypervirulent strain of K pneumoniae not typical of classic K pneumoniae variants. In this Grand Round, we review the clinical features of hypervirulent K pneumoniae and its link to invasive infections, and discuss the need for improved awareness and identification of the pathogen.

Introduction

Klebsiella are ubiquitous Gram-negative bacteria, which can be found in water, sewage, soil, on plants, and on the mucosal surfaces of mammals.1 From a medical standpoint, Klebsiella pneumoniae is the most important species of this genus, known to cause community-acquired and nosocomial infections worldwide. Unlike many other Enterobacteriaceae, K pneumoniae has a thick polysaccharide capsule shown to be an important virulence factor and aid in the avoidance of phagocytosis.2, 3 Over the past two decades, a distinct hypervirulent strain of K pneumoniae has emerged as a clinically significant pathogen responsible for highly invasive infections in both immunocompetent and immunocompromised individuals.4 This strain is best characterised by its hypermucoviscous phenotype secondary to abundant production of its polysaccharide capsule.4 In this Grand Round, we present a case of osteomyelitis due to hypervirulent K pneumoniae, review the clinical features of the pathogen, and discuss the need for clinicians to be aware that this organism is capable of causing severe invasive infections not typical of classic K pneumoniae variants.

Section snippets

Case presentation

A previously healthy 60-year-old Vietnamese man was admitted to a hospital in Atlanta, GA, USA, with a 1 month history of right leg and arm pain. Outpatient radiographs revealed lytic lesions of the right femur (figure 1) and right ulna suggesting a neoplastic process. The patient had been born and raised in Vietnam, and had moved to the USA to live with his family in Georgia 8 years before admission.

He was afebrile but had mild leucocytosis on admission. Open surgical biopsy sampling of the

Epidemiology and identification of hypervirulent K pneumoniae

Initial reports of cases of invasive infection due to the hypervirulent pathotype of K pneumoniae were from east and southeast Asia, although reports of cases from Canada, Europe, Israel, South America, and Australia have also been published in the past two decades, indicating that the pathogen is becoming more widespread.4, 15, 16, 17, 18, 19 Although prior cases of monomicrobial K pneumoniae liver abscess with metastatic spread that were suspicious for hypervirulent K pneumoniae had been seen

Conclusion

The present case illustrates an immunocompetent patient with primary hypervirulent K pneumoniae osteomyelitis. We performed further testing due to the striking clinical presentation of the infection as well as the hypermucoid nature of the isolates, which raised the suspicion for possible infection due to the hypervirulent strain. Whole-genome sequencing and additional PCR testing demonstrated the isolate to be a K1 genotype, ST23 strain expressing rmpA and rmpA2. Given the multiple reports of

Search strategy and selection criteria

We searched PubMed for papers in English published up to Feb 1, 2016, by using combinations of the following keywords: “Klebsiella pneumoniae”, “liver abscess”, “necrotizing fasciitis”, “osteomyelitis”, “hypermucoviscous”, “hypervirulent”, and “invasive”. Data surveyed included patient age and sex, underlying medical condition, type of infection, presence of hypermucoviscous phenotype, genotype, and serotype.

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