Health officials are investigating whether a potent virus that has infected hundreds of children nationwide killed a six-year-old boy in Arizona, officials said on Wednesday, adding that it would take more than a week to get an answer.

Officials said the tests are being conducted on the first-grader from Vistancia Elementary School in the Phoenix suburb of Peoria, to determine his cause of death and if he had been infected with the Enterovirus D68 (EV-D68) when he died.

"It's still too early to tell," said Jeanene Fowler, a spokeswoman for the Maricopa County Department of Public Health. "There are hundreds of respiratory diseases that could have caused this. No one is comfortable pinpointing any one of them right now."

The virus strain has infected nearly 700 people, most of them children, in 46 states and the District of Columbia since mid-August, according to the U.S. Centers for Disease Control and Prevention (CDC).

Two deaths in the U.S. have been directly linked to the strain of the virus, CDC officials said. At least four others who have died were infected with the enterovirus, but it is unclear what role it played in their deaths.

The unidentified boy in Arizona died on Tuesday from what officials described as a severe respiratory illness that had worsened over the weekend.

The death set off widespread concern at the 1,100-student school, with hundreds of kids being pulled from classes by their parents in the last two days.

Attendance plummeted by 50 percent on Tuesday and fell still lower on Wednesday, said Erin Dunsey, a spokeswoman for the Peoria Unified School District.

"Parents have a lot of questions. Unfortunately, we don't have a diagnosis to tell them right now," Dunsey said.

The school has disinfected every room at the school, wiping down desks, counter tops and other common surface areas. Hand washing and other hygiene protocols are being emphasized.

Health officials say the virus is transmitted through sneezes, coughs and contact with surfaces that have been touched by an infected person.