The pneumonia that infamously caused Hillary Clinton to stumble on Sunday—and launched a million headlines about the state of her health—may have spread within her campaign. Several of her top-level staffers have also contracted some sort of illness in the past few days, severe enough to make two seek emergency treatment.

“Everyone’s been sick,” a campaign source told People magazine, shortly after Clinton canceled a trip to California to recuperate this week.

Clinton, who was diagnosed with pneumonia on Friday and had started a course of antibiotics over the weekend, was only the latest casualty within her campaign. “At least half a dozen” staffers at the Brooklyn headquarters, including campaign manager Robby Mook, had reportedly been laid low by a “bug” going around. At least one staffer had been prescribed antibiotics before Clinton was diagnosed, and another had gone to the emergency room for dehydration problems. The campaign initially said Clinton, who left a Ground Zero memorial service for 9/11 victims on Sunday and was filmed stumbling into her van, was “overheated” at the event.

Clinton defenders spent Sunday arguing that candidates—and presidents—all suffer from occasional colds and flus, and they generally don’t disclose minor illnesses. The campaign’s treatment of the press drew criticism; the pool of reporters who travel with Clinton were left in the dark for hours after she was filmed stumbling, during which speculation ran rampant. Several factors could have exacerbated Clinton’s condition: her grueling schedule, replete with shaking the hands of every person she meets in several states; her high-stress lifestyle; and the added intensity of Donald Trump fanning rumors of her physical demise.