“Tonya told me that she met this new drug dealer on the street,” Carlyle said. “He gave her free drugs. He told her it was just a sample, but she never saw him again. She thought this was very unusual. And she was convinced his drugs gave her the terrible infection. She thought he was ‘cutting,’ as she called it, the drugs with some chemical contaminants. Apparently, drug dealers will do that to save money.”

Lopez felt more butterflies in her stomach. “Did she tell you anything else about him?”

“No, not really.” Carlyle shrugged. “Except to say that he had the darkest eyes she had ever seen in her life.”

“Dark as in color?”

Carlyle shook her head. “I think she meant it in the sense of opaque. She painted him as a scary person.”

Lopez’s chest thumped as she considered the implication of the accusation. She was so absorbed by the thoughts that she hadn’t even heard Carlyle’s next question.

“—don’t you think, Dr. Lopez?” Carlyle asked expectantly.

Dazed, Lopez looked back up at Carlyle. “I’m sorry, could you repeat the question?”

“If I just end up with a bit of a strep throat, it would be good news for everyone. Right? It would mean this bug doesn’t always cause terrible infections.”

Lopez nodded distractedly. “There are two types of group-A strep, or G.A.S., infections,” she said, beginning her rote explanation, her mind still dwelling on Tonya Jackson’s accusation. “First, there’s the more common, noninvasive form: strep throat, scarlet fever, mild skin infections, and so on. Second, is the much rarer invasive form. It causes infections like flesh-eating disease, toxic shock syndrome, and G.A.S. pneumonia.”

Carlyle frowned skeptically.

“Only a few subtypes of G.A.S. cause such invasive infections,” Lopez said, “but even with those strains, the bacterium still requires defects in the host’s own immune system before infection can develop. Do you understand?”

Carlyle nodded slowly, her brow creased in concentration. “You mean, even if you have the bad form of the bug, something has to be wrong with your immune system to get the bad disease?”

Lopez smiled vaguely. “Sort of. Though we can’t predict whom, only certain people are susceptible. That is why we see only clusters of flesh-eating disease rather than epidemics.”

Carlyle pointed at Lopez. “So this is good news.”

Lopez nodded. “But there is a downside.”

“How so?”

“It makes outbreak control much more difficult,” Lopez said. “Take measles, for example. Everyone infected demonstrates classic symptoms. They all get a rash. Although it’s highly contagious, we can quarantine those infected and protect the rest of the public.”

“And with this G.A.S. infection?”

Lopez shook her head. “People can become carriers without ever showing symptoms.”

“Carriers?” Carlyle grimaced in confusion.