History: An immunized 19 month-old boy with past medical history of asthma and environmental allergies presented to the emergency department with left wrist pain for four days and fever for two days. There was no preceding history of upper respiratory infection, trauma, tick bites, or arthritis of any other joints. There was no family history of MRSA or recurrent skin infections.
Physical examination: Vital signs on presentation were significant for temperature of 39.7 C and tachycardia to 192 bpm. Physical examination revealed erythema, tenderness, and swelling of the left wrist extending to the left hand, along with significantly restricted range of motion of the wrist. The remainder of the exam was within normal limits.
Laboratory or Diagnostic imaging or Procedures: Initial laboratory evaluation showed leukocytosis (WBC count 27,500/uL with 75% neutrophils), elevated inflammatory markers (ESR 54 mm/h, CRP 134.8 mg/L) and negative Lyme serology. Radiographs ruled out acute fracture and dislocation. Arthrocentesis of the left wrist showed purulent synovial fluid. MRI with and without contrast of the left upper extremity demonstrated moderate effusion in the left wrist with peripheral synovial enhancement. The enhancement extended along the ventral aspect of distal ulna and surrounding soft tissues (Image 1). Gram stain of synovial fluid showed presence of gram negative rods. Blood and synovial fluid cultures grew H. influenzae. Serotyping ultimately returned positive for H. influenzae a (Hia). Because of the rarity of invasive H. influenzae infections and the child's immunized status, immune work-up was pursued. Asplenia was ruled out with abdominal ultrasound. Serum studies revealed normal levels of lymphocyte subsets, immunoglobulin assay, varicella zoster IgG, Hib IgG, and Tetanus antitoxin IgG, though Streptococcus pneumoniae IgG (Danish system) levels showed suboptimal pneumococcal titers.
Final diagnosis: The patient was ultimately diagnosed with septic arthritis due to Hia and was treated with ceftriaxone.
Discussion:Widespread use of Haemophilus influenzae type b (Hib) conjugate vaccine has dramatically reduced the incidence of invasive Hib infections with resultant increase in non-type b and non-typeable serotype infections. Hia is a rare cause of septic arthritis and osteomyelitis in children, though its incidence in infants and among Native American and Alaskan Native populations has been rising. Hip and knee joints are most commonly affected. Similarity between the capsules of Hib and Hia may explain the severe presentation of invasive Hia infections. Invasive Hia infections may also be the presenting manifestation of asplenia, underscoring the importance of pursuing an immunodeficiency workup in children diagnosed with this infection. It is important to note that this patient's waning Streptococcus pneumoniae IgG levels do not represent evidence of immunodeficiency. It is well documented that individual response to pneumococcal vaccine is variable, as is the need for booster vaccination. Therefore, our case highlights the need to consider Hia as an emerging cause of invasive bone and joint infections in the post-Hib vaccine era. Early serotyping is important for isolating and containing invasive pathogens from a public health perspective.
