An outbreak of the flu among its bus drivers has forced the closure of all three public schools in Branchburg on Monday, district officials said.

More than 2,400 students attend Branchburg Central, Stony Brook and Whiton schools.

Students in the kindergarten-8th grade district attend Somerville High School. All schools in Somerville are open.

Branchburg Township School District Superintendent Rebecca Gensel said about one-third of the district's school bus drivers called out with the flu. She said district officials are working on a plan to provide transportation to students for the rest of the week.

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As of last week, Somerset County ranked 19th among the state's 21 counties with 3.7 cases per 10,000 people. There were 124 cases in the county.

A 4-year-old girl's flu-related death was the first in New Jersey this season. She lived in Central Jersey, but officials declined to say where.

Jeff Goldman may be reached at jeff_goldman@njadvancemedia.com. Follow him on Twitter @JeffSGoldman. Find NJ.com on Facebook.