study on bacterial contamination of office equipment 2006

Amazing, but true: telephones, keyboards and computer mice are in general many times dirtier than toilets.

A broadly based study in the USA on the subject of cleanliness at the work place has revealed the following average bacterial contamination per square inch:


Toilet seat                      49 bacteria/microbes

Mouse                        1676 bacteria/microbes

Keyboard                   3295 bacteria/microbe

Telephone               25,127 bacteria/microbes


Of course such horrifying conditions as those in the faraway USA are simply unthinkable in clean Switzerland - or are they?

In order to throw light on this question Neroform AG, the Swiss telephone disinfection company, carried out an appropriate study in Switzerland.


2006 study on bacterial contamination of office equipment in Switzerland

In March and April 2006 bacterial samples were taken from the office equipment of various companies and institutions in the cities of Zurich, Lucerne, Basle, Berne, Lausanne and Geneva, and then examined by the Qualis Laboratorium GmbH in Rubigen. In each case the following pieces of equipment were tested using so-called spread-plates.

·         PC keyboard: one swab each taken in the left-hand, centre, and right-hand areas

·         PC mouse: one swab

·         Telephone: one swab each top and bottom (earpiece/mouthpiece)

·         As a comparison, in some companies samples were also taken from the WC seat


In each case a total of around 600 samples was collected, before and after cleaning and treatment with the disinfectant.

After subsequent cleaning and disinfection samples were taken again, in order to obtain information about the effectiveness of the methods and products used. Apart from a few exceptions, after disinfection the pieces of equipment were largely germ-free. On average, over 98% of the germs observed before treatment were destroyed, which means that the appropriateness of the agents and methods used can be considered as established.


Bacterial contamination before disinfection (2006 Swiss study)

Before treatment, the number of microorganisms and germs which were living and capable of multiplying (spore-forming bacteria and moulds), converted to 1 cm2 in each case, as listed below was found. It should be noted that because of the test method using spread-plates and counting the bacterial cultures forming on them, only living microorganisms were recorded. Organisms which were already dead or no longer capable of multiplication were not recorded by the method used.



  Germs per 1 cm2  
Keyboard, left 3.28  
Keyboard, centre 3.31  
Keyboard, right (nummerical keypad) 2.57 ø Keyboard, mean 3.05
Mouse 2.59  
Telephone, top 4.26  
Telephone, bottom 2.45 ø Telephone, mean 3.35
Toilet seat (for comparison) 2.57  



At first sight the above figures may appear comfortingly low. However, these figures represent the number of living germs on a single square centimetre.


If the average number of germs on a keyboard is multiplied by the area of the keypad (excluding the F-key row), then another picture emerges:

·         On the keys of a keyboard a total of around 1040 living germs are roaming about

·         A mouse is home to an average of over 400 micro-organisms

·         The telephone, depending on size, provides space for 250 to 400 living bacteria.

The operators are in contact with all these pieces of equipment, constantly or repeatedly. And for the most part the operators are not aware that about as many, or indeed substantially more, living germs are to be found on the office equipment as on a toilet seat.

Contact plate with bacterial cultures


Comparison of 2006 Swiss study with 2004 study in the USA

According to a study carried out by Professor Gerba the following average levels of bacterial contamination were determined in the USA in 2004:

Toilet seat 49, mouse 1676, keyboard 3295, telephone 25,127 bacteria per square inch (= 6.45 cm2)

The figures from the USA are substantially higher than those recorded in Switzerland. Superficially one could draw the conclusion that conditions in clean Switzerland are simply essentially better than in the USA.

The differing results however stem from the different methods of measurement. In Switzerland traditional spread-plates (Rodac type, Caso agar with disinhibitor) were used to take the samples. The germ cultures which subsequently formed on the spread-plates were evaluated by the Qualis laboratory. With this method only living germs capable of multiplying are counted.

In the USA, on the other hand, the measurement was carried out using an electronic measuring device, With this method, in addition to the living bacteria, those which were already dead or incapable of multiplying were counted as well. In addition, traces and fragments of other parts and contaminations are also recorded. Significantly higher values therefore result with this method. These essentially higher values are not incorrect, but rather make clear the overall level of contamination of the equipment tested.

The results of the two studies cannot therefore be directly compared. If the values for living germs determined in Switzerland were extended with the other contaminations, then a picture similar to that in the USA would probably result.



Overall the level of contamination detected in Switzerland is considered by Dr G R Schnell of Qualis Laboratorium GmbH as giving cause for concern. The microorganisms can be transferred to the fingers and lead to infections if the fingers touch the mouth (licking the fingers, biting the finger nails etc.). Via the earpiece of telephones the germs transferred to the skin can lead to unusual reactions in the human being (from reddening of the skin to infections), especially where the immune system is deficient.

In order to stop the unhindered spread of germs (and pathogens from a wide variety of sources), regular cleaning and disinfection is considered appropriate. Where the equipment is used by several people, Dr Schnell considers cleaning and disinfection to be imperative!


Neroform AG services

Neroform AG has been cleaning and disinfecting telephone equipment since 1910, and since the 1980’s mice, keyboards and screens as well. We now also look after the clean internal life of your computers, as part of the dirt which collects there is distributed over the work place by the cooling fan.

So that you can also stop the formation of bacteria on your equipment between our cleaning visits (with thorough disinfection), we now also provide 4-part cleaning kits. These contain: Nerodata (for cleaning equipment), Nerovitro (screen), Neroform (disinfection), and also a drying cloth. These may be ordered via our homepage, under the heading Products.

You can access the price lists for our services and products in the appropriate sections of the homepage.


Test report Qualis Laboratorium GmbH