Despite the thyroid gland being extremely resistant to infection, it is still susceptible to infection by various bacteria. The cause can be almost any bacterium. Staphylococcus aureus, Streptococcus pyogenes, Staphylococcus epidermidis, and Streptococcus pneumoniae in descending order are the organisms most commonly isolated from acute thyroiditis cases in children. Other aerobic organisms are Klebsiella sp, Haemophilus influenza, Streptococcus viridans, Eikenella corrodens, Enterobacteriaceae, and salmonella sp. Occurrences of AIT are most common in patients with prior thyroid disease such as Hashimoto's thyroiditis or thyroid cancer. The most common cause of infection in children is a congenital abnormality such as pyriform sinus fistula. In most cases, the infection originates in the piriform sinus and spreads to the thyroid via the fistula. In many reported cases of AIT the infection occurs following an upper respiratory tract infection. One study found that of the reported cases of AIT, 66% occurred after an acute illness involving the upper respiratory tract. Although the rates of infection are still very low, cases of AIT have been on the rise in recent years due to the higher occurrence of immune-compromised patients. Other causes of AIT are commonly due to contamination from an outside source and are included below. * Repeated fine needle aspirates * Perforation of esophagus * Regional infection
Acute infectious thyroiditis
Subacute thyroiditis
Radiation-induced thyroiditis
Subacute lymphocytic thyroiditis
Hashimoto's thyroiditis
Ord's thyroiditis
Postpartum thyroiditis
Thyroid lymphoma