RALEIGH, N.C. (AP) — N.C. State University officials reported four new coronavirus clusters on Friday involving 51 cases in three sorority houses and one fraternity house, while another cluster was identified at the University of North Carolina at Chapel Hill.

In an email sent to students, N.C. State said one of the clusters was discovered at the Sigma Nu fraternity house, where 26 positive cases were reported. The school also said reports indicate a party was hosted at the house on Aug. 13.

The school said Delta Gamma sorority house had 15 positive cases, with six more positive cases at the Sigma Kappa sorority house. All three houses are located in the school’s Greek Village.

In addition, seven positive cases were reported at the off-campus Zeta Tau Alpha sorority house, according to the school. This week, N.C. State has reported seven coronavirus clusters, leading the school to announce on Thursday that it would move all undergraduate classes online starting Monday.

Also Friday, UNC-Chapel Hill alerted students, staff and faculty that a cluster of COVID-19 cases turned up at Carmichael residence hall. The school didn’t elaborate on how many cases were found in the residence hall. Six other clusters reported at the school were found at residence halls and fraternity houses. UNC-Chapel Hill switched to remote learning starting Wednesday.