Update on emerging infections: news from the Centers for Disease Control and Prevention. Hospitalized patients with novel influenza A (H1N1) virus infection--California, April-May, 2009.

[Ann Emerg Med. 2009;54:734-736.]

On June 11, 2009, less than 1 month after the release of this first report of hospitalized patients with novel influenza A (H1N1), the World Health Organization declared an influenza pandemic, urging the health care community to implement appropriate measures to help prevent a repeat of the deadly 1918 pandemic, which caused more than 50 million deaths. Although most cases observed during the current outbreak appear to be relatively mild (as of July 11, 2009, there were approximately 37,000 US cases, with slightly more than 200 deaths), serious complications have occurred and the pandemic remains in flux. Emergency physicians will play a pivotal role in the care of patients during this infectious disease outbreak and accordingly need to be armed with guidance to reduce morbidity and mortality and decrease likelihood of disease transmission. Key ED management issues include triage and isolation, diagnostic testing, and disposition. This discussion addresses these issues, which have also been the focus of recent guidance from American College of Emergency Physicians (ACEP) leadership.1, 2

Triage and Isolation

EDs act as major sites for transmission of respiratory viruses, as evidenced with severe acute respiratory syndrome. Seasonal influenza spreads principally by droplet transmission, ie, coughing or sneezing occurring over short (<6 feet) distances and less commonly by contact transmission (ie, skin to skin or fomite). Airborne transmission, ie, dissemination of small droplet nuclei or particles occurring over longer distances, is also believed to occur, but this mode remains controversial and is likely far less frequent. Limited data are available about transmission modes for novel influenza A (H1N1), but the CDC and others report that patterns are likely similar to those of seasonal influenza but with higher transmissibility.6, 7

Resources recently created and regularly updated by the CDC and ACEP have been made available to guide clinical decisionmaking.2, 8 Droplet precautions are advised for any patient presenting with “symptoms of an acute respiratory infection.” For waiting room patients, this means physical separation of symptomatic and asymptomatic patients, with distribution of surgical masks for those with active respiratory symptoms. Alternative temporary open-air waiting areas (eg, tents) are advised according to ED capacity. The triage process should include specific criteria to identify suspected cases among individuals with influenza-like illness, ie, temperature greater or equal to 37.8°C (100°F) plus cough or sore throat in the absence of a known cause other than influenza. Suspected cases are then identified as any patient with influenza-like illness who has had contact with anyone with a confirmed case, travel to a region with greater than 1 confirmed case, or residence in a community with greater than 1 confirmed case. Although early in the outbreak the CDC recommended airborne precautions with N95 mask use for health care workers caring for those with suspected or confirmed cases, guidelines have since evolved. The most recent ACEP and Society for Healthcare Epidemiology of America (SHEA) recommendations advise droplet precautions only, with the following exceptions: for patients requiring supplemental oxygen, add private room with closed door, and in instances in which respiratory procedures are being performed (ie, intubation, nebulizer treatment, suction, sputum induction), patients should be placed in an airborne isolation room.

Notably, a recent Morbidity and Mortality Weekly Report found that a significant proportion of health care worker–acquired cases of novel influenza A (H1N1) infections occurred among those with inconsistent use of personal protective equipment. The most common breaches were failure to adhere to eye protection, followed by failure to adhere to use of surgical or N95 masks.

Diagnostic Testing

Diagnostic tests available for influenza detection include those that are rapid (enzyme immunoassays or immunochromatographic assays). Rapid testing can be done at the bedside, with turnaround times of 10 to 30 minutes, but most EDs still rely on the central laboratory, resulting in turnaround times of 1 to 4 hours. An important limitation of rapid tests is their inability to distinguish between seasonal and novel influenza A (H1N1) viruses. There are also a variety of other slower but more sensitive and specific tests that require central laboratories for processing. These include direct immunofluorescence, polymerase chain reaction, serology, and viral culture.

In this Morbidity and Mortality Weekly Report, a significant number of false-negative rapid tests were reported. Notably, high rates of false-positive results have also recently been observed, a phenomenon known to occur early in any epidemic, when prevalence of disease is relatively low. Thus, although rapid antigen tests have the merit of timeliness, emergency physicians need to be aware of their limitations. For seasonal influenza, the sensitivity of commercially available rapid influenza tests ranges from 50% to 70%. As of yet, limited data are available about rapid test performance for novel influenza A (H1N1), although at least 1 recent study reports a sensitivity of only 10% to 30%. At Johns Hopkins Hospital (A. Valsamakis, oral communication), we have abandoned use of rapid testing according to similarly poor sensitivity.

Which ED patients should be tested is a complex and evolving issue. Currently, the CDC generically recommends testing persons if they have “an acute febrile respiratory illness or sepsis-like syndrome.” Guidelines also note that the very young, old, and immunocompromised may have atypical presentations. More practically for the ED, the CDC advises that those with “mild illnesses or those residing in affected areas need not be tested,” with priority given to those for whom hospitalization is being considered or those at high risk for complications. Testing of patients who will be admitted is important for isolation decisions (generally inpatient cohorting); testing in high-risk populations is important for treatment decisions.

Disposition

Disposition decisionmaking is critical for patient safety, hospital resource utilization, and control of nosocomial infections. At this point, there are insufficient data to reliably determine precisely who is at greatest risk for complications.13, 14 Both the CDC and ACEP thus suggest that risk-stratification decisions for novel influenza A (H1N1) be based on the same age and risk categories used for seasonal influenza. Younger children, older adults, immunocompromised individuals, nursing home patients, pregnant women, and those with chronic underlying diseases are considered at increased risk.

Although this early report suggests that most patients infected with novel influenza A (H1N1) in the United States have recovered quickly, with relatively short lengths of stay (median 2.5 days for those without underlying conditions), some prolonged hospitalizations and complications were observed. Not surprisingly, the majority occurred in those with chronic underlying conditions (see the table in the full CDC text for details). Several recent reports implicate that pregnancy and obesity are associated with increased risk of complications.15, 16 A surprising dearth of clinical prediction rules exist to aid disposition decisionmaking for those with seasonal influenza, with the exception of one that has been validated for adult patients older than 65 years. In that study, risk factors for hospitalization or death included increasing age, male sex, previous-year hospitalization for pneumonia or influenza, increased number of outpatient visits, and presence of pulmonary disease, cardiac disease, renal disease, dementia, stroke, or cancer. In a recent pilot study, we used influenza viral load as a surrogate to predict hospital length of stay. Future work is required to develop and validate clinical or biomarker prediction guidance for the novel influenza A (H1N1) infection. For now, emergency physicians should remain alert to ongoing clinical and epidemiologic data, local regulations, and the most up-to-date guidance from both the CDC and ACEP.