"Here we are," Loraine said as the elevator door opened. "Engineering is to the left."

In contrast to the elegant five-star hotel decor of the lobby, the fourth floor was the epitome of high-tech minimalist design. Everything was gleaming, high-gloss white, and the hallway was spotless. The women's shoes clicked on the composite flooring, and the sound echoed off the bare walls. There were no pictures, no bulletin boards, only closed white doors. The only color came from city-mandated institutional exit signs with red letters at either end of the lengthy corridor.

"I think I know why you are interested in seeing our HVAC system," Loraine said as they walked.

"Really?" Laurie questioned. She wasn't entirely sure herself.

What she knew of HVAC was the little she'd absorbed while the renovation of her and Jack's brownstone had been under way.

"You are thinking of airborne route of infection, which is another suggestion, as far as I am concerned, you are not the epidemiological amateur you profess to be. But let me reassure you, we have considered it also, and we have tested the water in the condensate pans for staph aureus on multiple occasions, including just this morning after yesterday's tragedy."

"Have any of the tests been positive?"

"No, none!" Loraine said emphatically. "Staph is not considered an airborne pathogen, but that did not stop us from considering it, and even though the tests were negative, we've drained all the pans and treated them."

"I didn't think staph was spread by the airborne route, either, Laurie said. "But the fact that a number of the cases seemed to have been primary pneumonias suggested the route of infection had to be airborne."

"I can't argue with that," Loraine said, "at least not from an academic perspective, but I can from a practical one. I chair an interdepartmental infection-control committee, which is just as its name suggests: interdepartmental. We have people from all departments, such as nursing, food service, engineering, and so forth. Currently, our representative from the medical staff is a surgeon, and when we were discussing the possibility of the staph being spread via the airborne route and believing the HVAC would be involved, he set us straight on an important fact. Patients undergoing endotracheal or laryngeal-mask-airway anesthesia, which all do in our hospitals when they have general anesthesia, neve: breathe operating-room air. The air they breathe always comes from the piped-in source."

"They never breathe ambient air?" Laurie questioned. There went her only theory as to how the MRSA victims were getting sick.

"Never!" Loraine confirmed.

Loraine stopped at one of the closed doors. An eye-level white plaque with incised black letters said: Engineering. "It's going to be a little loud in here," she warned.

Laurie nodded as Loraine pushed open the heavy insulated door. Once inside, Laurie scanned the large utilitarian high-ceilinged room. The walls and ceiling were concrete. A tangled web of piping, some insulated and some not, snaked out of various multicolored tanks and hung from the ceiling. Much larger ducts did the same after exiting or entering air handlers the size of small cars, each of which was mounted on rubber shocks.

"Anything in particular you'd like to see?" Loraine shouted.

"Which handlers service the ORs?" Laurie shouted back.

Loraine led Laurie down the relatively narrow walkway between the meticulously maintained equipment. Halfway to the opposite wall, Loraine stopped and patted the side of one of the air handlers. "This is the one. The coolant comes from the condensers on the roof, and the hot water comes from the furnaces in the basement."

"How do you access the condensate pan?"

"This access door," Loraine yelled. She grabbed the handle and had to pull hard to break the suction. When the door opened, they heard a whistling noise.

Laurie stuck her head into the opening and the wind wildly tossed her hair in all different directions. She had to grasp it to keep it out of her face.

"That's the condensate pan down there," Loraine shouted, while pointing over Laurie's shoulder to the base of the machine's innards.

Laurie nodded. She was interested because she knew airconditioning condensate pans were a frequent source of airborne outbreaks, such as Legionnaires' disease. She turned her head downstream into the mouth of the efferent duct, where she could see a mesh screen. "Is that a filter?" Laurie yelled.

"There are two," Loraine answered. She closed the door to the coils, and it snapped shut. She took several steps forward. There were two vertical slit-like openings. She pointed to the two of them with both index fingers. "The first is a standard filter for relatively large-sized particles. The second is a HEPA filter for particles down to the size of viruses. And to anticipate a question, we have on multiple occasions tested the HEPA filters for staph. Only twice did we get a positive result."

"Was it CA-MRSA?" Laurie questioned.

"It was, but it was not meaningful."

"Why?"

"Because the HEPA filter stopped it."

"What's that access door beyond the HEPA filter?"

"That's the clean-out port of the efferent duct. We have all the ducting cleaned once a year."

After about six feet, the efferent duct split like the tentacles of a squid into multiple smaller ducts, each going to a separate OR the PACU, and surgical lounge. Laurie could tell because each was labeled with an incised Formica plaque. Same as the main duct, each had a clean-out port. "When were the ducts cleaned last?"

"When the ORs were shut down."

Laurie nodded. Looking down toward the end of the walkway between the equipment, she saw another door. "Where does that door lead?"

"Another HVAC room, pretty much the same as this one except that it also houses our electrical generators. Beyond that is a doorway into a vestibule with a pair of service elevators and a back stairwell."

Laurie nodded again, and then walked back to the other side of the air handler that served the ORs. Similar to the efferent side, there was a clean-out port for cleaning the return duct. She then looked back at Loraine and shrugged her shoulders. "I can't think of any more questions. It's a very impressive system. And thanks for the lecture on air handlers. You seem to know your stuff."

"Part of our training in hospital infection control included learning more than we wanted to know about heating and ventilation," Loraine yelled. She then pointed back the way they'd come.

As soon as the heavy insulated door closed behind the women, the silence of the seemingly empty hospital enveloped them like an invisible blanket. Laurie tried to fix her hair, which at the moment gave her the appearance she'd been out riding in a convertible.

"I'd like to see a patient room," Laurie said. "Provided you have the time. I don't want to monopolize your afternoon."

"With as few patients as we have currently, I certainly have the time."

"How about David Jeffries's room."

"I think it's being thoroughly cleaned. We can look in, but I'm sure housekeeping will be there."

"Then another room will be fine."

Five minutes later, Laurie stood in one of the standard rooms.

In keeping with the five-star hotel decor in the lounge area, the room was equivalently decorated and furnished. The bed and the rest of the furniture were hardly the usual hospital issue. The television was a flat-screen model, which was set up without extra charge to have blue-ribbon cable service as well as Internet access. There was even an upholstered couch that unfolded into a bed in case a family member wanted to stay over. But what impressed Laurie the most was the bathroom. "Oh, my goodness," she said as she glanced in. It was done in marble and had a second flat-screen TV. "Do you have trouble getting some patients to leave?"