Acute conjunctivitis, also known as acute catarrhal conjunctivitis and commonly referred to as pink eye, is highly contagious. It is most often seen in the spring and autumn seasons. The infection can occur sporadically or can spread in community settings such as schools and factories. The onset of the disease is sudden, with an incubation period of one to three days. Both eyes may be affected simultaneously or one to two days apart. The inflammation is most severe three to four days after onset and then gradually lessens, with the course of the disease generally lasting less than three weeks. The most common pathogens are Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae. The pathogens can vary with the seasons; studies indicate that infections in the winter are mainly caused by Streptococcus pneumoniae, while Haemophilus influenzae conjunctivitis is more common in the spring and summer.