Sydney, Jan 5 (IANS) Some vacuum cleaners actually contribute to indoor air pollution by releasing dust and bugs that can spread infections and trigger allergies, reveals a study.

Lidia Morawska, professor at the Queensland University of Technology, and colleagues explained how previous studies showed that vacuum cleaners increase levels of fine particles and bacteria in indoor spaces, according to a university statement.

In an effort to provide more information about emission rates of bacteria and small dust particles, scientists tested a number of vacuum cleaners sold in Australia.

The vacuums came from 11 manufacturers, including those marketed for household and commercial use, ranged in age from six months to 22 years and cost from less than 100 dollars (Australian) to almost 800 dollars.

They looked at the effects that age, brand and other factors had on the amount of small particles and bacteria released into air — it was found that all the vacuums released some fine dust and bacteria into the air.

Surprisingly, vacuums with so-called High-Efficiency Particulate Air (HEPA) filters in some released only slightly lower levels of dust and bacteria.

Newer and more expensive vacuum cleaners were generally less polluting than older or less expensive models, the study showed.