7 Cross-Contamination Mistakes in Cleaning

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Cross-contamination is what happens when cleaning moves dirt and germs from one place to another without removing them. A surface can look clean and still have been wiped with what came off the restroom floor. It is the quiet failure of the cleaning trade, because nobody sees it happen.

Here are seven mistakes to look for, with the published guidance that explains each. Most of that guidance was written by the Centers for Disease Control and Prevention for health care facilities, where the stakes are highest, and one set of it was written for health care facilities with limited resources. We think the principles hold in an office, a store or a church as well. The seventh mistake is the one we wrote about ourselves in 2024, and it has a section of its own.

Mistakes with cloths

One cloth for the whole building

A cloth that has wiped a restroom counter should not go on to wipe a desk or a break room table. The CDC’s environmental cleaning procedures call for fresh cloths at the start of each cleaning session and for a cloth to be set aside once all of its sides have been used or it is no longer wet with solution (CDC). In practice that means a stack of clean cloths, with the restroom cloths kept apart from the rest.

Dipping a used cloth back into the solution

The same CDC procedures say it flatly: never double-dip cleaning cloths into portable containers of cleaning solution. The reason is easy to see. A used cloth returned to the bucket can put what it picked up into the solution, and the next surface is wiped with that.

Mistakes with mops

A mop head that is never changed

A mop touches every floor in the building, so a dirty one can spread what it is supposed to remove. The CDC’s recommendations for health care facilities are to change the mop head at the beginning of the day, and to clean mops and cloths after use and let them dry before they are used again (CDC). Its cleaning procedures add that mop heads and solutions are changed as often as needed, for example when visibly soiled, and at the end of each cleaning session, and that soiled mop heads are never left soaking in buckets.

Frequent mop head changes are one of the plain things we name in our own advertising, and the photograph shows a batch of our mop heads hung over a rail. If a building is mopped every night and the floor still smells, the mop is a good first thing to look at.

Cleaning in the wrong order

The CDC’s order of work is to proceed from cleaner areas to dirtier ones, to avoid spreading dirt and microorganisms, and from high to low, with floors last, so that what falls does not land on something already cleaned. Mop the restroom first and the same mop can carry the restroom into the lobby. Dust the shelves after vacuuming and the dust lands on a clean floor. In an office that means desks before the break room, the break room before the restrooms, and each room from the top down.

Mistakes with products and machines

Disinfecting a dirty surface, or wiping too soon

The CDC’s guidance for community buildings such as offices and gyms is to clean surfaces before sanitizing or disinfecting them, because impurities like dirt may make it harder for the chemicals to kill germs, and to keep a disinfected surface wet for the entire contact time given in the product’s directions (CDC). Spraying disinfectant onto a dirty counter and wiping it off right away does neither.

A vacuum that leaks dust

A vacuum takes dust in at the floor and has to keep it. The Carpet and Rug Institute advises replacing or emptying vacuum bags when they are half to two-thirds full, because that improves how well the vacuum works (CRI). The filter matters too. The Environmental Protection Agency describes a HEPA filter as one that can theoretically remove at least 99.97 percent of dust, pollen, mold, bacteria and other airborne particles 0.3 microns in size (EPA). We use HEPA vacuums, and we count vacuums with the proper bags and filtration among the plain things that make for a healthy facility.

Our own advice: keep the equipment with the building

The seventh mistake is carrying equipment from one building to the next. We wrote about it in 2024, and the advice has not changed.

It is always a good idea to make sure that your cleaning company is not bringing dirty, contaminated equipment to clean your office. A dirty mop, dirty rags or even a vacuum that was used at other facilities and then brought to yours can bring along millions of germs. If possible, provide the cleaning service with a custodial closet. That helps keep the equipment and supplies used to clean your office from becoming cross-contaminated with the last office’s germs.

A closet does not have to be large. A shelf for supplies, a hook or a rail where mop heads can dry, room for a vacuum and a cart, and ideally a mop sink nearby will do. In return, the mop that cleans your floor has cleaned only your floor.

How to check your own cleaning service

• Ask where the mops, cloths and vacuum were before they came to your building.
• Ask how often mop heads are changed and where they dry.
• Look in the bucket. Gray water left standing from the night before answers several questions at once.
• Ask whether restroom cloths are kept apart from the others.
• Check the vacuum for a bag that is the right one and is not full.
• Ask which products are used and how long the disinfectant is left on the surface.
• Smell the building first thing in the morning. If the place stinks and you have a cleaning service, maybe it is time to make a change.

The routine that avoids these mistakes, task by task, is on our page about janitorial services in Gilbert, AZ.

Questions people ask