Pope Francis met Sunday night with a Delaware family of four who were poisoned by a pesticide used in the condominium building where they stayed while on vacation in the Virgin Islands in March.

The unannounced encounter took place in the Atlantic Aviation terminal at Philadelphia International Airport before the pontiff boarded his plane for the trip home

The pope kissed and blessed the family, said Brian Tierney, whose communications company handled media for the World Meeting of Families.

Recovery from the neurological damage cause by the chemical has been agonizingly slow for Theresa Devine, Stephen Esmond and especially their two teenage sons, who suffered the worst effects.

The family fell ill on St. John's March 20 and paramedics found Esmond unconscious and the other family members suffering seizures.

Officials said they have been exposed to methyl bromide, a highly toxic pesticide that can cause convulsions, coma, and cognitive deficits and is banned for use indoors.

It had been sprayed in the condo below where the family was staying two days earlier, officials said.

After initial treatment, the four were flown to a hospital closer to their Wilmington home.

Devine, a dentist, was released first and is doing well physically, the family's lawyer, James Maron, told CNN earlier this month.

Esmond, an administrator at the Tatnall School in Wilmington, still suffers from tremors, struggles to speak and has difficulty turning the pages of books, Maron said.

The boys - who had been students and athletes at Tatnall - spent weeks in medically induced comas. They are conscious but can barely move, Maron told CNN.

"Neurologically, it's like being in a torture chamber," he said.

Both the Environmental Protection Agency and the Justice Department have launched investigations into potential illegal application of the pesticide in the Virgin Islands, a probe that has expanded to Puerto Rico. The pesticide, a neurotoxin, has been banned in many countries. The United States allows certain agricultural uses, but since 1984 it has not been legal to apply it in residential settings.

Terminix, the company whose employees used the pesticide, is slated to enter mediation Monday under the guidance of Ken Feinberg, who negotiated settlements for 9/11 victims, Maron said.