T.S. Elliot wrote that April is the cruelest month, but that didn’t account for flu season.

Winter, with its harsh weather that forces millions of people indoors for long periods, makes it especially bad for fighting off illnesses.

In addition, an estimated 30 percent of U.S. commercial buildings have poor indoor air quality, according to officials with Kimberly-Clark’s professional filtration division. That can lead to breathing problems, allergies, asthma and sick building syndrome.

“During the winter when everyone is trapped inside, airborne infections can spread when bacteria or viruses travel on dust particles or small respiratory droplets from an infected person’s sneezes or coughs,” said Robert Martin, associate category manager at Kimberly-Clark. “Healthy people can inhale the infectious droplets, or the droplets can land on their eyes, nose and mouth, increasing their chances of getting sick.”

Such problems can cut worker productivity by a third and cost businesses an estimated $160 billion annually, officials say.

To combat the problem, Kimberly-Clark offers these suggestions:

•          Pay attention to your HVAC system’s air filters. Air filters are a primary defense against indoor air pollutants. But air filters will only ensure good IAQ when they are maintained correctly. Replace filters according to the manufacturer’s schedule or use a pressure gauge to determine when the filter has reached its final pressure drop.

When installing filters, secure and gasket them tightly to avoid gaps between the filter frame and the filter rack. This helps avoid bypass air, which is detrimental to air quality because breathable particles travel through the gap without being filtered.

•          Look beyond the minimum efficiency reporting value to how effectively it filters submicron particles. The filtration efficiency of commercial air filters is rated by MERV, which is measured by the American Society of Heating, Refrigeration and Air-Conditioning Engineers’ 52.2 test standard, which provides the efficiency of the filter over three particle size ranges: E1 (very fine particles of 0.3 to 1 micrometers), E2 (fine particles of 1 to 3 micrometers), and E3 (coarse particles of 3 to 10 micrometers). The smallest (under 2.5 microns) and most toxic particles are most likely to travel to the deepest part of the lungs, where they can cause a variety of respiratory health problems.

Many filters have low efficiencies. Read the entire ASHRAE 52.2 test report, across all particle sizes.

•          Use filters with mechano-electret media to capture submicron particles. Filters that provide a good balance of mechanical and electret efficiency will almost always outperform a filter that relies solely on mechanical efficiency. While submicron particles are much smaller than the void spaces in most commercial electret media, the electrostatic effects are particularly useful in increasing the capture efficiency for the particles that can cause health problems.

“Improved indoor environmental quality may improve work performance, reduce absences and reduce healthcare needs,” Martin said, noting that IAQ improvements can reduce respiratory illnesses by up to 76 percent, and businesses can realize up to a 20 percent improvement in productivity. “Paying closer attention to your building’s air filtration system and its role in removing the tiny airborne particles that can cause health problems can help buildings improve their IAQ for better occupant health and productivity.”