Annals of Internal Medicine tip sheet for Feb. 28 early releases

According to experts, flu season 2012 is just beginning. Despite the late start, severe flu can be expected to affect up to five million people worldwide. While most patients recover, up to 500,000 will die, with the youngest and oldest being most vulnerable. Two new studies being published early online in Annals of Internal Medicine (www.annals.org) highlight the importance of rapid diagnosis and treatment of flu.

For patients who present with flu-like symptoms (fever, cough, sore throat), obtaining an accurate diagnosis is critical to patient management and infection control. Viral cultures are proven accurate, but turnaround from culture to lab result can take up to 10 days. Newer reverse transcriptase-polymerase chain reaction (RT-PCR) tests are much quicker than viral cultures, but they are very expensive and require specialized equipment. Rapid influenza diagnostic tests (RIDTs) are inexpensive and simple to use in the physician's office. However, little is known about their accuracy.

In the first Annals article, researchers reviewed 159 published studies to determine the accuracy of RIDTs in diagnosing flu in adults and children presenting with flu-like symptoms. In all studies, RIDTs were tested against one of two accepted reference standards. The researchers found that RIDTs were accurate at diagnosing the flu, but not as accurate at ruling it out, meaning that patients with a negative result would need to follow up with a culture or RT-PCR. RIDTs had an approximately 13 percent higher sensitivity in children compared to adults, and were more accurate at detecting the more common influenza virus A compared to influenza virus B. According to the authors, the study results make a case for implementing RIDTs in clinical practice, especially when treating children and other patients at risk for flu-related complications.

With an accurate flu diagnosis, physicians may choose to begin treatment with antivirals, In a second Annals study, researchers cited evidence that earlier treatment with antivirals (within 48 hours) may be of greater benefit than later treatment. The researchers reviewed 74 published observational studies to determine the benefits and harms of four commonly prescribed antivirals: oseltamivir, zanamivir, amantadine, and rimantadine. The researchers found that oral oseltamivir and inhaled zanamivir may provide a net benefit over no treatment for patients with known flu. Oral oseltamivir has been shown to reduce mortality and the duration of symptoms and complications of flu. On average, patient symptoms were reduced by about a day on oseltamivir versus no treatment. Researchers also found that inhaled zanamivir reduces signs and symptoms of flu, and could shorten the duration.