Once considered an unusual cause of pediatric infection, Kingella kingae has emerged as potentially the No. 1 cause of septic arthritis in the child younger than 24 months of age, according to Mary Anne Jackson, M.D., chief of pediatric infectious diseases at Children's Mercy Hospital, Kansas City, and professor of pediatrics at the University of Missouri-Kansas City.
This fastidious organism, which is often resistant to clindamycin, colonizes the oropharynx of approximately 15% of healthy toddler children. The problem is, it is difficult to grow on culture, requiring an enhanced isolation methodology and a little longer than normal (4.4 days) to grow. Knowing when to think about K. kingae as a potential pathogen should help guide treatment decision making.
The typical case involves a previously healthy and fully immunized toddler with a recent upper respiratory infection (URI) who presents with a high spiking fever and irritability. The next day, the child is limping.
What tip-offs might suggest that K. kingae should be considered as a potential pathogen, and how might this impact therapeutic decision making?
For the most part, this organism is an important cause of skeletal infection only in those less than 2 years of age. Other information that may be helpful includes the fact that concomitant URI or stomatitis occurs frequently in such patients (over half in one study), suggesting a respiratory or buccal source for the infection. And this organism has a predilection for ankle involvement in cases of arthritis and calcaneal involvement in bone infection.
Since K. kingae is extremely hard to grow on culture, request that the orthopedic surgeon place some of the purulent fluid into a blood culture bottle, in addition to plating for routine culture, Dr. Jackson recommended. Over a decade ago, physicians were alerted to the importance of using BACTEC blood culture bottles to isolate K. kingae in toddlers with skeletal infection (J. Clin. Microbiol. 1992;30:1278–81).
In that study, the investigators analyzed culture records for the period 1988–1991 and compared the performance of routine culture versus use of blood culture bottle for the recovery of pathogens. A diagnostic joint tap was performed in 216 children. Of those, 63 specimens grew significant organisms. Both methods were comparable for recovery of usual pathogens, but K. kingae isolates were detected by the BACTEC system only, in 13 of 14 specimens.
Just how often K. kingae is the culprit in infant septic arthritis is not completely clear since many centers have not routinely used the above technique to enhance growth, she added.
In a study conducted in Atlanta between 1990 and 1995, where joint aspirates were inoculated into thioglycolate broth, rather than blood culture, gram-positive bacteria were identified in 47 of 60 children (78%) younger than 3 years of age with culture-positive hematogenous septic arthritis and acute or subacute osteomyelitis, while gram-negative organisms were identified in 13 (22%).
Of those, K. kingae was cultured in 10 (17%); all of these cases occurred in children between the ages of 10.5 and 23.5 months. (J. Pediatr. Orthop. 1998;18:262–7).
More recent evidence implicates K. kingae in a cluster of skeletal infection in one day care center in Minnesota. Three cases occurred among children aged 17–21 months attending the same toddler classroom. Within the same week, all affected children had onset of fever, and antalgic gait. They all had preceding or concurrent upper respiratory illness. K. kingae was isolated from clinical specimens.
A colonization study was performed in response to the Minnesota outbreak. The investigators demonstrated that 13% of children at the index day care center (and 45% in the room where the cluster occurred) were colonized in the nasopharynx with K. kingae.
Interestingly, no day care center staff or children less than 16 months old were colonized. They compared the nasopharyngeal colonization results with a control day care center. Similarly, 16% of toddler age children were colonized (Pediatrics 2005;116:e206–13).
As the importance of recognizing K. kingae as a pathogen in the infant with skeletal infection is increasingly appreciated, clinical decision making in cases of pediatric skeletal infection is becoming more complex. Dr. Jackson suggested taking a collaborative approach with an infectious disease specialist and an orthopedic surgeon in order to focus on early diagnosis, pathogen isolation, prompt surgical drainage, and appropriate antimicrobial therapy.
Kingella kingae, shown in this Gram stain, is often resistant to clindamycin and is extremely hard to grow on culture. Courtesy Dr. Pablo Yagupsky