What are the 5 Most Dangerous Spots for Germs in the Home?

Story At-A-Glance

• A 2011 research paper says germs – particularly coliforms – can lead to disease are found in most homes.
• Researchers determined the area with the greatest concentration of germs within the home is the kitchen.
• In descending order of concentration – from highest to lowest – the five “germiest” spots in the home are the dish rag, the kitchen sink, the toothbrush holder, the pet bowl, and the coffee machine.

The Research Project

An independent, not-for-profit public health organization – NSF International – performed a research study in January of 2011. Twenty-two homes in a community in Michigan were observed in order to determine the dirtiest places in each for three types of germs.¹ They asked each of the participating 22 homes to perform a swabbing at very specific spots in the kitchen, bathroom, and specific items associated with their pets, electronics, kids, personal belongings, and even the family car.² In its research, NSF’s team of scientists looked for coliform bacteria, a large family of bacteria which includes E. coli, Salmonella, yeasts, molds, and Staphylococcus aureus (Staph) – another strain of bacteria.³ 

Classifying the Research

The researchers chose to summarize their findings using the following methods:

• • Evidence of germ type at the household – The researchers wanted to determine how many households contained each germ type. This was shown in their data as the percentage of households where they found evidence of each of the germ types on at least one of the 30 items.⁴ This was not a measure of how much or where it was found within each home, but simply a measure of whether it WAS found. For example, let’s assume the researchers found evidence of at least some Coliforms at 18 of 22 homes; they could then say that they found evidence of Coliform at 81% of the homes in the research project. This measurement, therefore, indicates nothing about WHERE in the home each type of bacteria was found, the quantity detected, or the amount found on each item. To find out WHERE and HOW MUCH bacteria was in each home, they used other methods of looking at the data.

• • Coliform Danger Spots per household – The researchers then wanted to be more specific regarding Coliforms. When they observed the data they found evidence of Coliforms at the majority of homes – 18 of 22 homes. To clarify the “WHERE” from the previous point, they created the “Coliform Danger Spots per household” measurement. This identified “WHERE” Coliforms were most often found in households in which Coliforms were detected.⁵ In this study, the researchers detected Coliforms at 18 of 22 homes, and at 14 of these 18 homes it was found on the dish rag. Therefore, the researchers concluded that in homes where they detected Coliforms, 77% of the time it was found on the dish rag. Therefore, the researchers concluded that a particularly dangerous spot for Coliforms to be found in the home is on the dish rag.

• • Coliform / yeast / mold per household – The researchers also wanted to be more specific when determining the amounts of yeast and mold.⁶ In the homes where these substances were detected, the researchers used this method to indicate which items within the home showed evidence on their surfaces of not only  yeast and mold, but also Coliforms. It appears that the researchers were attempting to confirm that if yeast and mold are found on an item, it is also likely to contain Coliforms. Let’s assume the researchers found evidence of at least some yeast or fungus at 7 of 22 homes, and that at 6 out of these 7 homes, they found Coliforms, yeast and/or mold on the dish rag. The researchers would then conclude that they found Coliforms, yeast, and/or mold 86% of the time on the dish rag in homes where they detected yeast and/or mold.

• • Germ counts on each household item – Finally, once the researchers had determined where the germs were found in the homes, they wanted to know the amount of contaminants on each item. They did this by determining the average count of germs they found on each item type.⁷ 

Research Findings

Using these methods, the researchers determined: 

• • Evidence of germ type at the household – researchers detected Coliforms at 81% of households, yeast / mold at 31% of households, and Staph at about 5% of the homes.⁸

• • Coliform per household – in homes where Coliforms were detected, they were most often found in the kitchen on the dish rag and kitchen sink.⁹

• • Coliform / yeast / mold per household – in homes where yeast and mold were detected, the combination of yeast, mold, and Coliforms was most often located in the kitchen on the dish rag and in the coffee reservoir.¹⁰ The combination was also quite common on the toothbrush holder, pet toys, pet bowl, computer keyboard, video game controller, and TV remote control.¹¹

• • Germ counts on each household item – perhaps the most important statistic is this measurement. Yes, a homeowner may have detected germs on various items within his or her home, but this does not answer whether he or she should be concerned about it. As one reviews the survey, the top 5 germiest items in the home are the dish rag, kitchen sink, the toothbrush holder, pet bowl, and the coffee machine.¹² Other items may have germs on them, but they have no where the concentration.¹³

Comment

The first point the reader should note is that the number of homes used in the research group seems somewhat small. For simplicity, it is assumed that the research study is adequately designed and reflective of other North American homes. Assuming that one lives in North America, then he or she can make some inferences on his or her home.  First, he or she can infer different germ types – particularly Coliforms – that can lead to disease are found in most homes, and they are most likely in his or her home. The key issue for the reader is to determine how concerned the average homeowner should be regarding this issue. Secondly, the homeowner can infer from the research that the most dangerous spot for germs in the home is in the kitchen. Thirdly, it seems the most relevant finding from the research is how concentrated the germ becomes at a specific location within the home. Finally, as one reviews the concentration table within the research paper, one can justifiably conclude that any cleaning should focus on the most dangerous locations for germs within the home, and the five “germiest” spots in the home are the dish rag, kitchen sink, the toothbrush holder, the pet bowl, and the coffee machine.