NEW YORK — You probably clean vigorously at home, at least occasionally. But how often does this happen at work, the valiant efforts of the janitorial staff notwithstanding?

Maybe not as effectively as you might wish or suspect, according to a five-city study of germs found in office settings.

Charles Gerba, a microbiologist at the University of Arizona, collected samples from office buildings in Atlanta, Chicago, New York City, San Francisco and Tucson, Ariz., last fall to determine how much human parainfluenza 1 virus was present. The virus is responsible for common respiratory infections, such as pneumonia and bronchiolitis.

The survey collected samples from common areas: telephone mouthpieces, computer mice, desktops, doorknobs and handles, conference rooms, light switches and office cubicles.

New York -- where half of all office surfaces contained the virus -- was the most virus-laden city, followed by Atlanta, San Francisco, Chicago and Tucson.

Conference rooms were found to have far fewer germs than cubicles, while desktops had the most of the tested surfaces. In all office buildings, the light switch was the least contaminated site.

Surfaces sampled included the telephone mouthpiece, computer mouse, desktop, doorknob/handles and light switches in offices, cubicles and conference rooms

The study involved 328 surfaces and was conducted with a grant from Clorox Co., the Oakland, Calif.-based maker of cleaning products.