Jan 6 (Reuters) - As the United States grapples with a flu season that has killed 21 people so far, the Food and Drug Administration on Tuesday cleared the way for greater use of a molecular test designed to quickly detect the presence of the virus in a nasal swab.

The test, made by Alere Inc, can now be used in a wide variety of clinical settings, including doctors' offices, emergency rooms, clinics and other healthcare facilities. Previously, it could only be used in a limited number of laboratories.

The FDA first cleared the Alere i influenza A & B test in June as a prescription-only device, categorizing the test as moderately complex and therefore not to be used widely.

The agency said it agreed to allow wider use of the test after the company submitted data showing its ease of use and low risk of false results when used by untrained operators.

"Today's decision allows the first nucleic acid-based test to be available in clinical settings that previously could not use this technology," said Alberto Gutierrez, director of the FDA's Office of in Vitro Diagnostics and Radiological Health.

Nucleic acid tests are designed to detect the presence of genetic material from the virus. Alere's test produces results in as little as 15 minutes and can be conducted in front of the patient.

Flu symptoms are caused by two types of virus: Type A and Type B. Infections can range from mild to severe. More than 200,000 people in the United States are hospitalized with flu-related complications each year, according to the CDC.

Shares of Alere rose 1.4 percent to close at $37.25 on the New York Stock Exchange.

(Reporting by Toni Clarke in Washington; Editing by Bernard Orr)