Specific Real-Time Polymerase Chain Reaction Places Kingella kingae as the Most Common Cause of
Osteoarticular Infections in Young Children
Background: The use of universal 16S rDNA polymerase chain reaction (PCR) has recently shown that the place of
Kingella kingae in osteoarticular infections (OAI) in young children has been underestimated, but this technique is not
the most sensitive or the most rapid method for molecular diagnosis. We developed a specific real-time PCR method
to detect K. kingae DNA and applied it to the etiologic diagnosis of OAI.

Patients and Methods: All children admitted to a pediatric unit for OAI between January 2004 and December 2005
were enrolled in this prospective study. Culture-negative osteoarticular specimens were tested by 16S rDNA PCR and
by K. kingae-specific real-time PCR when sufficient sample remained.

Results: By culture alone, a pathogen was identified in 45% of the 131 specimens tested (Staphylococcus aureus, n =
25; K. kingae, n = 17; others, n = 18). 16S rDNA PCR and K. kingae-specific PCR were both applied to 61 of the
culture-negative samples. The combination of culture and 16S rDNA PCR identified a pathogen in 61% of cases (K.
kingae DNA, n = 16; DNA of other microorganisms, n = 5). Specific real-time PCR identified a further 6 cases caused
by K. kingae and confirmed all 16 universal PCR-positive cases, bringing the overall documentation rate to 66%. K.
kingae was the leading cause of OAI in this pediatric series (n = 39, 45%), followed by S. aureus (n = 25, 29%)

Conclusion: The K. kingae-specific real-time PCR places K. kingae as the leading cause of OAI in children at our
Pediatric Infectious Disease Journal. 26(5):377-381, May 2007
Kingella organisms colonize the human respiratory tract. They cause skeletal infections, endocarditis, and bacteremia,
and rarely pneumonia, epiglottitis, meningitis, abscesses, and ocular infections.   Kingella are short, nonmotile, gram-
negative coccobacilli that occur in pairs or short chains. The organisms are slow-growing and fastidious. Kingella are
recovered from the human respiratory tract and are a rare cause of human disease.  Among Kingella species, K.
kingae is the most frequent human pathogen. K. kingae frequently colonizes the respiratory mucous membranes.
Children between 6 mo and 4 yr have the highest rates of colonization and invasive disease from this and other
respiratory tract pathogens such as Moraxella catarrhalis and Streptococcus pneumoniae. Infection shows a seasonal
distribution, with more cases in fall and winter.  The most common manifestations of K. kingae disease are skeletal
infections, endocarditis, and bacteremia. Other rare infections include pneumonia, epiglottitis, meningitis, abscesses,
and ocular infections.  The most common skeletal infection is septic arthritis, which most frequently affects large,
weight-bearing joints, especially the knee and ankle. Osteomyelitis most frequently involves the bones of the lower
extremity. Onset is insidious, and diagnosis is often delayed. Hematogenous invasion of the intervertebral disk can
occur and has been most commonly reported in the lumbar intervertebral spaces.  Kingella endocarditis has been
reported in all age groups. Endocarditis may involve both native and prosthetic valves. Kingella is a component of the
so-called HACEK group (Haemophilus aphrophilus and Haemophilus parainfluenzae, Actinobacillus, Cardiobacterium,
Eikenella, Kingella—see Gram-Negative Bacilli: HACEK Infections), which includes fastidious bacteria capable of
causing endocarditis.