Outbreaks of Invasive Kingella kingae Infections in Daycare Facilities: Approach to Investigation and Management

Pharyngeal Colonization by Kingella kingae, Transmission, and Pathogenesis of Invasive Infections: A Narrative Review

With the appreciation of Kingella kingae as a prime etiology of osteoarticular infections in young children, there is an increasing interest in the pathogenesis of these diseases. The medical literature on K. kingae’s colonization and carriage was thoroughly reviewed. Kingella kingae colonizes the oropharynx after the second life semester, and its prevalence reaches 10% between the ages of 12 and 24 months, declining thereafter as children reach immunological maturity. Kingella kingae colonization is characterized by the periodic substitution of carried organisms by new strains. Whereas some strains frequently colonize asymptomatic children but are rarely isolated from diseased individuals, others are responsible for most invasive infections worldwide, indicating enhanced virulence. The colonized oropharyngeal mucosa is the source of child-to-child transmission, and daycare attendance is associated with a high carriage rate and increased risk of invasive disease. Kingella kingae elaborates a potent repeat-in-toxin (RTXA) that lyses epithelial, phagocytic, and synovial cells. This toxin breaches the epithelial barrier, facilitating bloodstream invasion and survival and the colonization of deep body tissues. Kingella kingae colonization and carriage play a crucial role in the person-to-person transmission of the bacterium, its dissemination in the community, and the pathogenesis of invasive infections.

Clinical presentations of Kingella kingae musculoskeletal infections in South Australian children

AIM

This study aimed to alert clinicians to the spectrum of presentations of Kingella kingae musculoskeletal infections.

METHODS

Between August 2010 and March 2018, 55 children presented with positive K. kingae polymerase chain reaction on joint fluid, bone or deep soft tissue collections involving the limbs and subsequently underwent retrospective medical record, radiological and laboratory review. Demographics and clinical information are presented.

RESULTS

Median age at presentation was 15.9 months (range 4.3 months-10.7 years) and 64% were male. Septic arthritis was the most common diagnosis (95%), median duration of symptoms was 4 days, 65% had a preceding infection (e.g. upper respiratory or gastrointestinal) and 22% re-presented to emergency departments after prior discharge. The lower limb was involved in 84%, with the knee being most affected (55%). If the lower limb was involved, 82% of previously weight-bearing children had a limp or were unable to weight bear. On presentation, median temperature was 36.7°C and inflammatory markers were mildly elevated. No blood cultures grew K. kingae. Five synovial fluid cultures were positive for K. kingae. Plain radiography showed effusion, soft tissue swelling or a lesion in 53% of patients. All 41 ultrasounds showed effusion, soft tissue swelling or synovial thickening. One patient with delayed diagnosis later presented with avascular necrosis of the femoral head.

CONCLUSION

Kingella kingae is difficult to diagnose due to non-specific symptoms, absence of fevers and often unremarkable blood tests. Despite generally having good long-term outcomes, our case of avascular necrosis suggests accurate diagnosis and treatment are important.

Review highlights the latest research in Kingella kingae and stresses that molecular tests are required for diagnosis

AIM

The aim of this study was to provide an update on paediatric Kingella kingae infections.

METHODS

We used the PubMed database to identify studies published in English, French and Spanish up to 15 November 2020.

RESULTS

Kingella kingae colonised the oropharynx after the age of 6 months, and the mucosal surface was the portal of entry of the organism to the bloodstream and the source of child-to-child spread. Attending day care centres was associated with increased carriage rate and transmission and disease outbreaks were detected in day care facilities. Skeletal system infections were usually characterised by mild symptoms and moderately elevated inflammation markers, requiring a high clinical suspicion index. The organism was difficult to recover in cultures and molecular tests significantly improve its detection. Kingella kingae was generally susceptible to beta-lactam antibiotics, and skeletal diseases and bacteraemia responded to antimicrobial, leaving no long-term sequelae. However, patients with endocarditis frequently experienced life-threatening complications and the case fatality rate exceeded 10%.

CONCLUSION

Kingella kingae was the prime aetiology of skeletal system infections in children aged 6-48 months. Paediatricians should be aware of the peculiar features of this infection and the need to use molecular tests for diagnosis.

Outbreaks of Kingella kingae Infections in Daycare Centers Suggest Tissue Tropism of the Causative Strains

BACKGROUND

Although Kingella kingae is recognized as an important pediatric pathogen, our knowledge of the virulence factors involved in the invasion of specific host's tissues is limited. Outbreaks of K kingae infections in daycare centers represent natural experiments in which a single virulent strain, introduced into a cohort of susceptible young children, causes multiple infections. If K kingae strains exhibit tissue tropism, the syndromes observed in a given cluster of cases would be relatively homogeneous.

METHODS

Clinical data of all the K kingae outbreaks known to date were gathered and analyzed. The clinical syndromes diagnosed in the affected attendees were classified as septic arthritis, osteomyelitis, tenosynovitis, soft tissue infection, bacteremia with no focal disease, endocarditis, and meningitis, and computed separately. To assess the similarity of the clinical syndromes detected within outbreaks, we used the Cramer V statistic, which is a measure of the association between 2 nominal variables and, for the purposes of the study, between the detected clinical syndromes and the outbreaks.

RESULTS

A total of 23 outbreaks involving 61 attendees were identified. The mean±SD attack rate in the affected classrooms was 15.8% ± 4.8%, and the K kingae colonization rate among the attendees was 54.8% ± 25.3%. Seventy-two separate foci of infection were diagnosed. Osteomyelitis and septic arthritis were the most common clinical syndromes and were diagnosed in 26 children each, followed by tenosynovitis in 4 children. The clinical syndromes diagnosed among attendees to the same classroom showed a statistically significant tendency to be similar (P = .015).

CONCLUSIONS

The distribution of clinical syndromes in clusters of K kingae infections differs from that of sporadic cases. The causative strains combine enhanced virulence and high transmissibility, and show tropism toward bones, joints, and tendon sheaths. This information can be used to identify virulence factors associated with invasion of these specific host tissues.

Management of an outbreak of invasive Kingella kingae skeletal infections in a day care center

BACKGROUND

Kingella kingae (Kk) is frequently responsible for invasive skeletal infections in children aged 3-36months. However, few outbreaks of invasive Kk infections in day care centers have been reported. The objective of the present study was to describe (a) the clinical and laboratory data recorded during an outbreak of invasive Kk skeletal infections, and (b) the management of the outbreak.

METHOD

Four children from the same day care center were included in the study May and June 2019. We retrospectively analyzed the children's clinical presentation and their radiological and laboratory data. We also identified all the disease control measures taken in the day care center.

RESULTS

We observed cases of septic arthritis of the wrist (case #1), shoulder arthritis (case #2), knee arthritis (case #3) ans cervical spondylodiscitis (case #4). All cases presented with an oropharyngeal infection and concomitant fever prior to diagnosis of the skeletal infection. All cases were misdiagnosed at the initial presentation. The mean (range) age at diagnosis was 10.75months (9-12). The three patients with arthritis received surgical treatment. All patients received intravenous and then oral antibiotics. In cases 1 and 2, Kk was detected using real-time PCR and a ST25-rtxA1 clone was identified. The outcome was good in all four cases. Four other children in the day care center presented with scabies during this period and were treated with systemic ivermectin. The Regional Health Agency was informed, and all the parents of children attending the day care center received an information letter. The day care center was cleaned extensively.

CONCLUSION

Our results highlight the variety of features of invasive skeletal Kk infections in children and (given the high risk of transmission in day care centers) the importance of diagnosing cases as soon as possible.

The first report on epidemiology of oropharyngeal Kingella kingae carriage in Scandinavian children: K. kingae carriage is very common in children attending day care facilities in Western Norway

Kingella kingae colonizes the upper airways in children and has been recognized as the most common causative agent of osteoarticular infections (OAI) in children below 4 years of age. This is the first Scandinavian study to investigate oropharyngeal K. kingae carriage in healthy children. From June 2015 to August 2016, we recruited 198 healthy children aged 11-14 months from routine consultations at health promotion centers in Hordaland County, Norway for a cross-sectional study. After their parents had provided informed consent; demographic data were registered, and an oropharyngeal swab was collected. The oropharyngeal swab was analyzed with a real-time PCR assay specific to K. kingae targeting the RTX toxin locus. Results showed an asymptomatic carriage rate of 12.6%. A striking and highly significant difference was observed between the children that had started attending day care facilities as compared with children still being at home (33.33% vs 8.5%; p < 0.001). K. kingae is prevalent in young children in Norway. This study emphasize that K. kingae should be considered an important etiological agent in OAI. Transmission seems to be facilitated in day care facilities. The correlation between oropharyngeal carriage and OAI needs to be further explored.

A New Highly Sensitive and Specific Real-Time PCR Assay Targeting the Malate Dehydrogenase Gene of Kingella kingae and Application to 201 Pediatric Clinical Specimens

Kingella kingae is a significant pediatric pathogen responsible for bone and joint infections, occult bacteremia, and endocarditis in early childhood. Past efforts to detect this bacterium using culture and broad-range 16S rRNA gene PCR assays from clinical specimens have proven unsatisfactory; therefore, by the late 2000s, these were gradually phased out to explore the benefits of specific real-time PCR tests targeting the groEL gene and the RTX locus of K. kingae However, recent studies showed that real-time PCR (RT-PCR) assays targeting the Kingella sp. RTX locus that are currently available for the diagnosis of K. kingae infection lack specificity because they could not distinguish between K. kingae and the recently described Kingella negevensis species. Furthermore, in silico analysis of the groEL gene from a large collection of 45 K. kingae strains showed that primers and probes from K. kingaegroEL-based RT-PCR assays display a few mismatches with K. kingae groEL variations that may result in decreased detection sensitivity, especially in paucibacillary clinical specimens. In order to provide an alternative to groEL- and RTX-targeting RT-PCR assays that may suffer from suboptimal specificity and sensitivity, a K. kingae-specific RT-PCR assay targeting the malate dehydrogenase (mdh) gene was developed for predicting no mismatch between primers and probe and 18 variants of the K. kingae mdh gene from 20 distinct sequence types of K. kingae This novel K. kingae-specific RT-PCR assay demonstrated high specificity and sensitivity and was successfully used to diagnose K. kingae infections and carriage in 104 clinical specimens from children between 7 months and 7 years old.

Defining the Mechanical Determinants of Kingella kingae Adherence to Host Cells

Kingella kingae is an important pathogen in young children and initiates infection by colonizing the posterior pharynx. Adherence to pharyngeal epithelial cells is an important first step in the process of colonization. In the present study, we sought to elucidate the interplay of type IV pili (T4P), a trimeric autotransporter adhesin called Knh, and the polysaccharide capsule in K. kingae adherence to host cells. Using adherence assays performed under shear stress, we observed that a strain expressing only Knh was capable of higher levels of adherence than a strain expressing only T4P. Using atomic force microscopy and transmission electron microscopy (TEM), we established that the capsule had a mean depth of 700 nm and that Knh was approximately 110 nm long. Using cationic ferritin capsule staining and thin-section transmission electron microscopy, we found that when bacteria expressing retractile T4P were in close contact with host cells, the capsule was absent at the point of contact between the bacterium and the host cell membrane. In a T4P retraction-deficient mutant, the capsule depth remained intact and adherence levels were markedly reduced. These results support the following model: T4P make initial contact with the host cell and mediate low-strength adherence. T4P retract, pulling the organism closer to the host cell and displacing the capsule, allowing Knh to be exposed and mediate high-strength, tight adherence to the host cell surface. This report provides the first description of the mechanical displacement of capsule enabling intimate bacterial adherence to host cells.IMPORTANCE Adherence to host cells is an important first step in bacterial colonization and pathogenicity. Kingella kingae has three surface factors that are involved in adherence: type IV pili (T4P), a trimeric autotransporter adhesin called Knh, and a polysaccharide capsule. Our results suggest that T4P mediate initial contact and low-strength adherence to host cells. T4P retraction draws the bacterium closer to the host cell and causes the displacement of capsule. This displacement exposes Knh and allows Knh to mediate high-strength adherence to the host cell. This work provides new insight into the interplay of T4P, a nonpilus adhesin, and a capsule and their effects on bacterial adherence to host cells.

A modified multilocus sequence typing protocol to genotype Kingella kingae from oropharyngeal swabs without bacterial isolation

BACKGROUND

Outbreaks of Kingella kingae infection are an emerging public health concern among daycare attendees carrying epidemic clones in the oropharynx. However, genotyping of such epidemic clones from affected cases is limited by the low performance of current methods to detect K. kingae from blood samples and lack of specimens available from infected sites. We aimed at developing a modified multilocus sequence typing (MLST) method to genotype K. kingae strains from oropharyngeal samples without prior culture. We designed in silico MLST primers specific for K. kingae by aligning whole nucleotide sequences of abcZ, adk, aroE, cpn60, recA, and gdh/zwf genes from closely related species belonging to the Kingella and Neisseria genera. We tested our modified MLST protocol on all Kingella species and N. meningitidis, as well as 11 oropharyngeal samples from young children with sporadic (n = 10) or epidemic (n = 1) K. kingae infection.

RESULTS

We detected K. kingae-specific amplicons in the 11 oropharyngeal samples, corresponding to sequence-type 6 (ST-6) in 6 children including the epidemic cases, ST-25 in 2 children, and 3 possible novel STs (ST-67, ST-68, and ST-69). No amplicon was obtained from other Kingella species and N. meningitidis.

CONCLUSIONS

We herein developed a specific MLST protocol that enables genotyping of K. kingae by MLST directly from oropharyngeal samples. This discriminatory tool, with which we identified the first K. kingae outbreak caused by ST-6 in Europe, may be used in further epidemiological investigations.

Investigation of Kingella kingae Invasive Infection Outbreaks in Day Care Facilities: Assessment of a Rapid Genotyping Tool Targeting the DNA Uptake Sequence

Outbreaks of Kingella kingae invasive infections have recently been reported in day care centers. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) revealed that although the invasive strains had widespread dissemination in the day care population, less virulent strains were also circulating in the facilities. However, these typing tools are costly, time-consuming, and labor-intensive and provide delayed results. A study was conducted to assess the performance of a rapid and cost-effective genotyping tool targeting the DNA uptake sequence (DUS) in the investigation of outbreaks of K. kingae disease. DUS typing (DUST) patterns of each strain from 7 different clusters were compared to distinguish genotypically linked strains from others. PFGE and, when available, MLST results were used as gold standards. DUST was assessed on 80 K. kingae isolates from Nir-Itzhak (n = 14), Tel-Nof (n = 14), Palmahim (n = 5), Umm-al-Fahm (n = 7), Eilat (n = 8), Nevatim (n = 15) in Israel and Paris, France (n = 17). A unique DUST pattern was involved in the Nir-Itzhak, Palmahim, Umm-al-Fahm, and Paris episodes. Two DUST patterns were found in Eilat, whereas at least 3 were identified in the Tel-Nof and Nevatim episodes. In total, 11 (13.8%) children carried a K. kingae isolate that differed from the outbreak strain. These results were concordant with those obtained with the traditional PFGE and MLST methods. DUST appears to be sensitive and specific in distinguishing the invasive outbreak strain from others in asymptomatic carriers and could be useful to limit unnecessary exposure of the entire day care population to selective antibiotic pressure.