A study presented at last week’s national infectious diseases meetings generated lots of media interest because it looked at an issue that many people ask about all the time – how well, and how long, do germs stick around on surfaces like those in your home? Unfortnately, because of the way the researchers did the study, we don’t have an absolutely clear answer yet, but there are some clues that reinforce all the advice I’ve given previously in this GERMBlog and in Chapter 9 of the book, Germ Proof Your Kids – The Complete Guide to Protecting (without Overprotecting) Your Family from Infections (ASM Press, Washington, D.C., 2008).
There were 2 parts of the study. In the first, people who had colds due to rhinoviruses (the most common, but by no means the only, cause of the common cold) were asked to name the surfaces in their homes that they had touched frequently in the past day – the usual suspects were named (doorknobs, phones, remote control devices, refrigerator handles, light switches, salt and pepper shakers, etc). The researchers then tested those surfaces for cold viruses and found them on many of the surfaces tested. Here’s the reason that this doesn’t give us an absolute answer to the “how well, how long” question – the test the scientists used was a test for a “footprint” of the virus (the genetic material, or RNA, of the virus), not the living virus itself. So, even though the virus footprint was detectable as long as a day or more on the surfaces after contact with a sick person, we don’t know if touching the surfaces could result in an infection (with a living virus).In fact, the second part of the study suggested that, as I’ve written previously here and in the Germ Proof Your Kids book, viruses only stay ”alive”, and therefore “infectious” for an hour or two on a dry surface. In that second part of the study, the researchers took the patient’s own mucous and “spiked” it with virus from the lab. They then smeared the “spiked” mucous onto common household surfaces (ahh, the beauty of science!!) and found that although the footprint (RNA) of the virus transferred to hands touching the surface for as long as 2 days, living (infectious) virus was only transferred to about 25% of hands at 1 hour after smearing the surface, and almost not at all by 24 hours.
A parallel report at the same meeting essentially found the same results in pediatricians’ offices where toys and surfaces tested positive for virus footprints (not living, infectious viruses). I’ve also told you about the doctor’s office “hot zone” for catching infections in Chapter 9 of Germ Proof Your Kids – The Complete Guide to Protecting (without Overprotecting) Your Family from Infections.
Viruses, as is true for all other germs, live longer in moist environments. Moist surfaces, like bathroom sinks and toilets, kitchen sinks, and laundry areas, may harbor living viruses for many hours – even a day or more. But, dry surfaces probably only sustain living, infectious, virus germs for minutes to an hour or two. Having said that, though, the studies presented last week remind us of the importance of home hygiene because germs do transfer from people to surfaces and do stay there long enough to potentially infect the next person to touch that surface. There are well-proven home “hot zones” (page 282 of Germ Proof Your Kids) where disinfecting surfaces can be expected to reduce the chances of catching an infection – especially during a time when someone at home is ill. But it’s not just during sick days – home kitchens just like yours are responsible for more than 90% of Salmonella infections in this country (see August 3, 2008 post of Dr. Rotbart’s GERMBlog)! Salmonella is a bacterium, not a virus, and bacteria can live on surfaces, wet and dry, much longer than viruses.
What can you do to make your home, and everyone who lives there, healthier? Establish a regular schedule for disinfecting your home. In Chapter 9 of Germ Proof Your Kids – The Complete Guide to Protecting (without Overprotecting) Your Family from Infections, I recommend the following schedule:
Kitchen sinks and countertops – daily
Bathroom sinks, countertops, flush handles – 3-4 times/week
Toilets, Kitchen floors, Bathroom floors – weekly
Bedroom and playroom of a sick family member – 2 times/day
Finally, there is an important difference between “cleaning” and “disinfecting”. Disinfecting kills germs on contact, whereas cleaning works by washing away the germs that can be washed away. You should use a disinfecting product for most household hygiene. In Germ Proof Your Kids, I recommend using a disinfecting product that contains bleach. Bleach, unlike other disinfectants that only kill bacteria (“antibacterial”), kills bacteria and viruses. Viruses are the most common cause of household infections, far outnumbering the cases of bacterial infections in the home.