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SARS surge during flu season could spell chaos in health care
CDC scrambling to prepare guidance, will push flu shots
Concerned that severe acute respiratory syndrome (SARS) may resurge as a seasonal infection, the Centers for Disease Control and Prevention (CDC) is rapidly developing strategies and tools to help clinicians make the differential diagnosis between the emerging disease and annual influenza, Hospital Infection Control has learned.
"Will SARS corona virus be seasonal?" asked John Jernigan, MD, a medical epidemiologist in the CDC division of healthcare quality promotion.
"We know that other human corona viruses do tend to be seasonal. They peak in the fall and winter with other respiratory viruses and decline in the spring, just as we have seen basically with this outbreak. It begs the question whether will we see a new wave of disease coming with the upcoming respiratory virus season. I think it behooves us to assume that that is going to happen and be prepared for it when it does happen," he emphasized.
Jernigan and other CDC SARS investigators recently discussed the looming situation in San Antonio at the annual conference of the Association for Professionals in Infection Control and Epidemiology (APIC).
If SARS resurges as a seasonal illness, the challenge will be recognizing it among the flu and other viral illnesses that could present almost identically in a crowded emergency department this fall. How similar are they? Recall that when SARS first emerged it was described widely as a "flulike" illness.
Influenza symptoms can include fever, muscle aches, headache, lethargy, dry cough, sore throat, and runny nose. The fever and body aches can last three to five days, and the cough and lack of energy may last for two or more weeks. Even in the absence of SARS, influenza can be difficult to diagnose based on clinical symptoms alone because the initial symptoms of flu can be similar to infections caused by Mycoplasma pneumoniae, adenovirus, respiratory syncytial virus, rhinovirus, and parainfluenza viruses.
"We are not only going to see influenza; we are going to see other respiratory infections," said Denise Cardo, MD, a medical epidemiologist in the CDC division of healthcare quality promotion. "The hospitals will need to have a system to rule out SARS and [identify patients] who need to be isolated. Our division is working with the [CDC] division of quarantine. We are tying to come up with plans to help institutions do specific things like checklists for them to consider — not just guidelines, but specific tools to help them be prepared for the fall."
The current case definition of SARS includes such symptoms as fever, cough, shortness of breath, and difficulty breathing. Epidemiologic criteria — which may become increasingly critical during flu season — include travel within 10 days of onset of symptoms to an area previously linked to transmission of SARS. The conundrum is that even as the CDC is urging heightened vigilance to prevent SARS from emerging in the United States, the agency is well aware that such surveillance efforts will be complicated considerably by even just an average flu season.
"I think it is going to be very difficult, and I think it could really change the way that we manage people with respiratory illness as they present to our health care facilities," Jernigan told Hospital Infection Control. "I think people are going to have to really look hard at their triage procedures. They are going to have to be alert and educate patients to, No. 1, identify themselves if they have respiratory symptoms."
But not all SARS cases present with dramatic respiratory symptoms; the latest CDC case definition (June 5, 2003), as we go to press, includes "asymptomatic or mild" respiratory illness.
"We think that the peak of transmission may be in the second week of illness, but it is clear that some transmission does occur very early — even before they develop respiratory symptoms," Jernigan said. "This is a problem, and it is something that we need to take into account in our infection control precautions."
One obvious strategy will be to urge flu vaccination for the public and try to motivate historically apathetic health care workers to get immunized. "This should be an encouragement for people to get vaccinated," Cardo told HIC. "Because if we really push vaccination and we can prevent flu, then we won’t see as many cases of flu in health care settings. It will help all of us. I hope we can have [more] health care workers vaccinated. About 35% of health care workers get vaccinated for flu. It’s very, very low. So I am hoping SARS will be a way to promote influenza vaccination for health care workers and patients."
Another strategy will be to use rapid diagnostic tests to confirm or rule out flu, she adds. A variety of flu tests now are available, including some that provide results within 24 hours. Still, that will not completely solve the situation because most of the rapid tests have a sensitivity of about 70% for detecting influenza. That means as many as 30% of samples may be inaccurate by rapid tests. As currently recommended by the CDC, initial diagnostic testing for suspected SARS patients should include chest radiograph, pulse oximetry, blood cultures, sputum Gram’s stain and culture, and testing for influenza A and B, and respiratory syncytial virus. A specimen for Legionella and pneumococcal urinary antigen testing also should be considered, the CDC recommends. Clinicians should save any available clinical specimens (respiratory, blood, and serum) for additional testing until a specific diagnosis is made.
The difficult key
"The big problem in most of the centers around the world that have had transmission has been early recognition and isolation of patients. This is the key — recognize these patients and isolate them early," Jernigan told some 2,000 APIC attendees. "I didn’t say it was easy; I said it is key. It is a very nonspecific illness, and it is very difficult to distinguish from other common illnesses. We have to have heightened suspicion. We have to modify our triage procedures so that we will pick these people up the moment they walk into our hospitals and clinics — so we can get a mask on them and get them in an appropriate place where they can be evaluated."
The CDC currently recommends that clinicians evaluating suspected SARS cases should use standard precautions (e.g., hand hygiene) together with airborne (e.g., N95 respirator), contact (e.g., gowns and gloves), and eye protection. Again, that may be a difficult protocol to follow during flu season, but SARS has shown the ability to spread explosively after only minor breaches. (See HIC, June 2003, under archives at www.HIConline.com.)
"Most of the transmission around the world seems to have occurred through close contact, most commonly to health care workers and household contacts," Jernigan said. "We can’t overemphasize the importance of nosocomial transmission in these outbreaks. Hospitals have really served as an amplifier of this outbreak. That is why infection control is so critical and is going to be the key to controlling transmission."
The primary mode of transmission is via large droplets or direct contact with the patient, he said. "Some patients appear to be able to transfer this virus very efficiently, while the lion’s share of people do not." Airborne transmission cannot be ruled out in certain cases, particularly those involving aerosol-generating procedures, he said.
Fomite transmission from environmental surfaces also may be a factor. Some laboratories in Asia have found that the virus can persist as long as one to two days after drying on environmental surfaces, Jernigan said.
"We need to do more work in that area to confirm those data," he added. "You can do a lot of things with viruses in the laboratory, but it certainly is concerning that the environment could play a role in transmission."
Anatomy of an emerging infection
SARS has an incubation period of about four to six days, usually followed by a sudden onset of fever, chills, headache, and malaise. "Colleagues in Canada report that fever might not even be present at the beginning," Jernigan said. "They have one or two days of just headache, malaise, and myalgia before the fever actually starts. But it usually is not until three to seven days after the onset of symptoms that they get any respiratory symptoms, which is important to remember if we are going to recognize these people early."
SARS may have an enteric phase with diarrhea, but this has not been universally reported. However, shortness of breath is a common symptom of SARS. "Other things of interest that may be helpful in picking these people out is upper respiratory tract symptoms such as sore throat are less common amongst patients with documented corona virus infection," Jernigan said.
The illness often progresses slowly, with the more severe manifestations in the second week. At 14 to 16 days, infections often are at their most severe, and patients who are going to become severely ill will degenerate further from that point.
About 15% of cases will require mechanical ventilation. The case fatality rate, as with flu, is much higher in the elderly. Though annual flu deaths dwarf the impact of SARS thus far, there is no vaccine for the corona virus and antivirals used against the flu have not shown any efficacy.
"We know that this is a completely novel, heretofore undescribed corona virus," Jernigan said. "There are two other corona viruses that cause disease in humans. They basically cause the common cold. But again, this virus seems to be very distantly related."
The current thinking is that civet cats and other exotic animals sold in Chinese markets may be asymptomatic hosts of the virus. "They isolated the virus [in animals], and these appear to be very closely related to the human SARS virus," he said. "Could these animals have been the reservoir for transmission to humans? There are reports of seroconversions in animal handlers that deal with these animals all the time."
Though the new SARS agent is different from its known corona cousins, there are concerns it will behave in a similar manner with regard to the changing seasons. It bears repeating that the other two human corona viruses peak during the fall and winter months.
"We need to assume this is going to come back," he said.