ACCHUU! This common sound has recently turned into a warning signal for people all over the country.

This winter, the United States is experiencing the worst flu outbreak since the 2009 swine flu epidemic. The Center for Disease Control and Prevention (CDC) has reported that 47 states out of the 50 have experienced widespread flu activity. Cities, including Boston, Massachusetts, have declared a state of public health emergency as hospitals are becoming filled to capacity with flu victims.

This season’s strain of flu, which has been identified as H3N2, has been proven to be one of the most severe, in relation to deaths and hospitalizations. While California is facing high numbers of flu cases, experts predict that the worse may be still yet to come, according to CBS News.

The flu has hit many Upper School students already, contributing to a significant number of recent absences.

“The number [of absences] has gone up quite dramatically,” Administrative Attendance Officer Sue Prutton said. “Usually, I might have around 30 absences per day, and right now we are up to about 60. Most absences are actually due to the flu or doctor’s appointments concerning illnesses, so we are really seeing a huge increase in the number of sick students.”

Similarly, nurse Debra Knott has had more students come to her office in recent weeks, although the reason for their visits is not solely the flu.

“While we have definitely been seeing an increase in the number of cases of the flu on all three campuses, most of the sick students are actually suffering from common colds. We are lucky that the numbers haven’t been that high, like other places,” she said.

While H3N2 is quickly spreading, especially in school environments, it is important to note the difference between the common cold and the flu. According to Knott, the flu has a sudden, intense onset, accompanied by a high fever, while a normal cold builds up gradually and does not cause high temperatures.

Nevertheless, the administration and nurse encourage students to take the flu shot if they have not already done so, as it can reduce the chances of flu onset by up to 60 percent.

Besides vaccination, the nurse recommends washing hands more often and avoiding touching one’s face as much as possible. She also encourages students to stay home if they are experiencing flu-like symptoms, especially if they have a fever, to prevent contamination.