In certain situations, confirmation of etiology by laboratory testing is required in order to guide the initiation and duration of antiviral therapy, and for the implementation of infection control measures and surveillance. Other benefits of influenza virus detection are the reduction of inappropriate antibiotic use, decreased length of stay in emergency departments, and fewer additional laboratory studies, all leading to a reduction in health care costs [1••] . The Centers for Disease Control and Prevention (CDC) and the Infectious Diseases Society of America (IDSA) have published guidelines to better define patients who should undergo influenza testing [1••, 2••]. The available methods include immunological techniques (i.e. rapid antigen-based tests, immunofluorescence assays, serologic testing), molecular techniques (i.e. reverse-transcriptase polymerase chain reaction [RT-PCR]), and microbiological techniques (i.e. viral cultures). While RT-PCR has the highest sensitivity and specificity, rapid antigen and immunofluorescence testing, though very useful as initial screening tests, are considerably less sensitive. Besides, the sensitivity and specificity of any of these techniques will vary depending on the laboratory equipment, personnel expertise, the timing of recollection, and the appropriate handling of the samples [1••, 2••]. Respiratory specimens can be obtained by many different methods including throat swabs, nasal aspirates, and nasopharyngeal swabs, aspirates and washing [2••] . In mechanically ventilated subjects, more invasive maneuvers such as endotracheal aspirates and bronchoscopic or non-bronchoscopic bronchoalveolar lavage (BAL) may be required in order to obtain adequate lower respiratory tract samples. While rapid antigen tests, immunofluorescence and RT-PCR all can yield results quick enough to guide point-of-care clinical decisionmaking, serologic tests and viral cultures provide retrospective diagnosis, availability only in reference laboratories, and usefulness when confirming screening test. For this reason, they are normally reserved for epidemiological and research purposes (Table 2) .