Klebsiella pneumoniae is a common bacterium found in various environments, including soil, water, and on human mucous membranes, particularly in the gastrointestinal tract and upper throat. While typically an opportunistic pathogen, causing infections primarily in hospitalized or immunocompromised individuals, a more aggressive variant, hypervirulent Klebsiella pneumoniae (hvKP), has emerged as a significant public health concern. This distinct strain exhibits an enhanced capacity to cause severe, life-threatening infections, even in previously healthy individuals, marking a shift from the typical profile of classic Klebsiella pneumoniae (cKP). The World Health Organization (WHO) has highlighted the increasing reports of hvKP, particularly strains that are also multidrug-resistant, emphasizing the growing threat this bacterium poses globally.
Defining Hypervirulence
Hypervirulent Klebsiella pneumoniae (hvKP) distinguishes itself from classic Klebsiella pneumoniae (cKP) through specific biological and genetic characteristics. A notable feature is its enhanced capsule production, often resulting in a “mucoid phenotype.” This increased capsule is linked to genes like rmpA and magA, which regulate the mucoid phenotype and increase virulence.
The hypermucoviscous phenotype, a hallmark of hvKP, can be identified through a “string test.” If a bacteriological loop stretches a bacterial colony on an agar plate to form a viscous string greater than 5 millimeters, the isolate is hypermucoviscous. This characteristic reflects the bacterium’s enhanced ability to resist immune responses like phagocytosis, making it more invasive.
Unlike cKP, which typically affects individuals with underlying health conditions, hvKP possesses enhanced invasiveness, allowing it to infect healthy individuals in the community. It also has a heightened capacity to cause bloodstream infections, contributing to widespread damage. While initial hvKP strains were often susceptible to antibiotics, increasing reports show hvKP acquiring antibiotic resistance, complicating treatment.
How It Affects the Body
Hypervirulent Klebsiella pneumoniae can cause severe, rapidly progressive infections, often more aggressive than classic strains. A hallmark infection is primary liver abscess, which can occur without predisposing hepatobiliary disease. These abscesses can be dangerous and may lead to metastatic complications, meaning the infection spreads to other organs.
Beyond liver abscesses, hvKP causes severe eye infections, specifically endophthalmitis, which can lead to vision loss or blindness. The bacterium can also invade the central nervous system, causing meningitis, an infection of the membranes surrounding the brain and spinal cord. These neurological infections require prompt medical attention.
Other severe infections include necrotizing fasciitis, often called “flesh-eating disease,” which causes rapid soft tissue destruction. HvKP can also cause severe pneumonia and bloodstream infections (sepsis), which can quickly become life-threatening if not addressed swiftly. Its ability to spread to multiple body sites underscores its heightened virulence and systemic threat.
Who Is at Risk and How It Spreads
Hypervirulent Klebsiella pneumoniae (hvKP) distinguishes itself from classic Klebsiella pneumoniae (cKP) by infecting not only immunocompromised individuals but also those previously healthy. While individuals with underlying conditions like diabetes, liver disease, or cancer remain at increased risk, hvKP’s capacity to cause severe infections in otherwise healthy people is a notable concern. This broadens the susceptible population compared to cKP, which primarily affects hospitalized patients with comorbidities.
HvKP transmission occurs through several routes. Person-to-person spread is common, especially in healthcare settings via contaminated hands of healthcare workers or environmental surfaces and equipment. This highlights the importance of rigorous infection control in hospitals and long-term care facilities.
Beyond healthcare environments, hvKP can be acquired in community settings, although exact mechanisms are not fully defined. Potential routes include exposure to contaminated food or water, and person-to-person contact among close associates. The global spread of hvKP has been observed, with infections initially reported predominantly in the Asia-Pacific Rim, particularly Taiwan, but now increasingly recognized worldwide due to travel and increased movement of people.
Managing and Preventing Infections
Rapid and accurate diagnosis is foundational for managing hypervirulent Klebsiella pneumoniae (hvKP) infections. Early identification allows timely intervention, which is crucial given the aggressive nature of these infections. Laboratory capacity for molecular testing and detection of specific virulence genes, in addition to resistance genes, is recommended for reliable identification.
Treatment primarily involves antibiotics, but this is complicated by increasing antibiotic resistance in hvKP strains. While earlier hvKP strains were often susceptible, a growing number are acquiring resistance to various antibiotic classes, including carbapenems, considered last-resort antibiotics. The emergence of carbapenem-resistant hvKP (CR-hvKP) necessitates aggressive and early intervention, often requiring combination therapy with multiple antimicrobial agents. Options may include newer agents like ceftazidime/avibactam, especially for resistant strains.
Prevention of hvKP infections relies heavily on robust infection control measures, particularly within healthcare settings. Rigorous hand hygiene practices among healthcare workers are paramount to limit person-to-person spread. Proper disinfection of surfaces and equipment also plays a significant role in preventing the transmission of the bacterium.
Isolation precautions for infected patients are implemented to contain the spread within healthcare facilities. Establishing and maintaining effective surveillance systems are important for detecting and controlling outbreaks of hvKP. Furthermore, responsible antibiotic stewardship in both healthcare and community settings is a broad strategy aimed at limiting the development and spread of antibiotic resistance, thereby preserving the effectiveness of existing treatments against hvKP and other bacterial threats.