We searched PubMed for papers published between Jan 01, 1970, and June 30, 2012, by using combinations of the following keywords: āKlebsiella pneumoniaeā, āliver abscessā, āendophthalmitisā, and āmeningitisā. We selected articles published in English or Chinese. We selected reports of large case series for inclusion in this Review in favour of anecdotal reports, of which we identified many. Data surveyed included ethnic origin, underlying diseases, clinical manifestations, treatments, and
ReviewKlebsiella pneumoniae liver abscess: a new invasive syndrome
Introduction
Klebsiella pneumoniae is a well known human pathogen. However, a distinct invasive syndrome has been detected in southeast Asia in the past two decades.1, 2 Liver abscesses in patients infected with K pneumoniae were first described in the 1980s in anecdotal reports and case series from Taiwan.2, 3 Extrahepatic complications resulting from bacteraemic dissemination, including endophthalmitis,3 meningitis,4 necrotising fasciitis,5 and other illnesses,6 have also been recorded. The invasive syndrome was subsequently reported in many southeast Asian countries, including Singapore,7, 8 Hong Kong,9, 10 Korea,11, 12 and Vietnam.13, 14 Few cases were reported from China.15 Findings from a meta-analysis showed that the prevalence of K pneumoniae infection has been increasing since the late 1980s, and that it is now the main cause of liver abscess in Hong Kong,10 Singapore,8 South Korea,11 and Taiwan.2
The reasons for the predominance of this syndrome in Asian people are unclear. In 2002, Ko and colleagues16 showed that the major factor was the microbe itself. K pneumoniae isolated from Asian patients with the invasive syndrome had distinct phenotypic and genotypic featuresāeg, when assessed in mouse models, it was much more virulent than were strains isolated from patients from outside Asia.16 Moreover, a genotype strongly associated with this highly invasive disease is widespread worldwide.17, 18, 19
In the past two decades, this syndrome has been described in anecdotal reports from North America.20, 21 Most patients from outside Asia with this invasive syndrome were of Asian descent. However, in the past decade, cases in patients of non-Asian descent are now being reported in North America and South America, and the isolated strains of K pneumoniae have been classified as serotypes K1 and K2.17, 19 In this Review, we describe the epidemiology, clinical manifestations, diagnosis, and treatment of liver abscesses caused by K pneumoniae.
Section snippets
Definition of the invasive syndrome
First, we propose a case definition for this newly described invasive liver abscess syndrome, to allow clear identification of cases. As knowledge about this distinct aspect of infection with K pneumoniae accumulates, this definition can be modified (panel).
The invasive nature of some K pneumoniae strains includes a hypermucoviscous phenotype associated with serotypes K1 and K2 and the regulator of mucoid phenotype A gene (rmpA). A loss or reduction of capsule synthesis will decrease a strain's
Epidemiology and risk factors
In the past decade, 38 patients were diagnosed as having a liver abscess caused by K pneumoniae in two case series in the USA.21, 24 South Korea has the second highest prevalence of K pneumoniae liver abscesses (Taiwan has the highest prevalence), with 321 patients identified in two national studies.11, 12 We reviewed the demographic and clinical characters of 512 patients from four large-scale studies in Taiwan (table 1).25, 26, 27, 28 Nearly all patients had community-acquired infections.
Virulence factors
Several virulence factors have been described for K pneumoniae, and include the presence of the capsular serotype, mucoviscosity-associated gene A (magA), rmpA, and aerobactin (table 2).43 K pneumoniae strains expressing capsular type K1 or K2 antigen are especially virulent. These serotypes have a high prevalence of resistance to phagocytosis and intracellular killing by neutrophils and bactericidal complements in a patient's serum. Mutant strains without a capsule are highly susceptible to
Clinical manifestations and diagnosis
The most common clinical manifestations in patients with K pneumoniae liver abscesses are fever, chills, and abdominal pain.25, 26, 27, 28 Nausea and vomiting occur in about a quarter of patients.25, 26, 27, 28 However, these symptoms are not characteristic for the K pneumoniae invasive syndrome. Leucocytosis, thrombocytopenia, increased concentrations of C-reactive protein and glucose in blood, and abnormal results of liver function tests were common.27
In terms of clinical diagnosis, in
Management
Because of the potential for metastatic infection, clinicians should assess patients for such complications when clinical response is poor. Strict glycaemic control can prevent the development of metastatic complications.35
The selection of antimicrobial treatment should be based on in-vitro susceptibilities and clinical response. Cephalosporins are the antibiotic mainstay of treatment in Asia for K pneumoniae abscesses (table 3).11, 12, 25, 28 Patients in the USA were treated successfully with
Conclusions
This invasive syndrome seems to be spreading to countries outside Asia. Presentation of liver abscess with bacteraemia in patients infected with K pneumoniae strains that have a positive string test result (figure) can be the first clinical clue. Rapid diagnosis followed by appropriate treatment should improve a patient's outcome and prevent metastatic complications, which are severe. Further research should aim to find out why Asian populations (particularly Taiwanese people) are especially
Search strategy and selection criteria
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