WASHINGTON (Reuters) – Several flu-like viruses are more common than usual this flu season in the United States, adding to the misery and confusion caused by H1N1 swine flu, one lab company said on Tuesday.

Kansas City, Missouri-based ViraCor Laboratories found that only 6 percent of the samples it was sent tested positive for influenza A virus. Tests by the U.S. Centers for Disease Control and Prevention show virtually all influenza now circulating is H1N1 swine flu.

The rest include a range of flu-like viruses, each caused by a distinct germ but all causing similar symptoms.

By far the most common is rhinovirus, one of the so-called common cold viruses, the testing company found.

This fits in with a report last November from Children’s Hospital of Philadelphia, where 500 children were hospitalized with rhinovirus in September and October — an unusually high number to be that sick with a normally mild virus.

ViraCor, which tested samples from severely ill pediatric patients around the country, as well as transplant and other high-risk patients who became ill, found that 28 percent of the tests showed the patient had rhinovirus between April and December this year.

The tests also showed that:

* 39.5 percent of tests from children up to age 3 had rhinovirus. The figure fell to 23 percent among 11- to 18-year-olds and less than 20 percent of adults.

* 4.2 percent of patients tested had metapneumovirus but 6 percent of children under 10 had metapneumovirus.

* 3.2 percent of children 3 and under had respiratory syncytial virus or RSV; it was rare among older children.

* 6 percent of children under 3 who were tested had parainfluenza virus, as well as 6 percent of patients over 61. The virus was rare among age groups in between. “Overall, parainfluenza rates are much higher than expected,” the company’s report said.

* 1.5 percent had adenovirus.

Doctors rarely test patients for respiratory viruses, in part because few tests are available and in part because there is little option for treatment other than keeping patients comfortable, breathing and hydrated.

Antibiotics can be used for bacterial infections but are useless against viruses.

But better tests are now being developed for flu and ViraCor’s xTAG RVP test can diagnose 12 different viral infections.