Acute infectious thyroiditis (AIT) also known as suppurative thyroiditis, microbial inflammatory thyroiditis, pyrogenic thyroiditis and bacterial thyroiditis. The thyroid is normally very resistant to infection. Due to a relatively high amount of iodine in the tissue, as well as high vascularity and lymphatic drainage to the region, it is difficult for pathogens to infect the thyroid tissue. Despite all this, a persistent fistula from the piriform sinus may make the left lobe of the thyroid susceptible to infection and abscess formation. AIT is most often caused by a bacterial infection but can also be caused by a fungal or parasitic infection, most commonly in an immunocompromised host. Signs and symptoms In most cases AIT is characterized by onset of pain, firmness, tenderness, redness or swelling in the anterior aspect of the neck. Patients will also present with a sudden fever, difficulty swallowing and difficulty controlling the voice. Symptoms may be present from 1 to 180 days, with most symptoms lasting an average of about 18 days. The main issue associated with the diagnosis of AIT is differentiating it from other more commonly seen forms of thyroid conditions. Pain, fever and swelling are often much more severe and continue to get worse in people who have AIT compared to those with other thyroid conditions. Causes 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