The University of Arizona Learn About Germs


UA College of Public Health






Germs In The Home Environment

Microorganisms in The Bathroom

Bathroom Mold

Water and mold growth are interrelated variables, making bathrooms a hot spot for exposure in the home environment.  Although fungal spores are present everywhere, it is when dampness and moisture are uncontrolled that fungi grow and develop into visible mold.

Indicators that mold might be present in the bathroom are: absent exhaust fan, water or moisture damage, and visible mold in the shower or elsewhere in the bathroom.

Behaviors in reducing mold growth:

  • Open windows in bathroom while showering
  • Use exhaust fan
  • Wipe shower walls with towel
  • Turn on fan or space heater
  • Dehumidifiers
  • Leave uncarpeted
  • Remove indoor organic sources such as plants, wood, and paper products.
  • Mold removal from items in the home

    1. Use bleach solution to clean mold on hard surfaces
    2. Open windows if possible to ventilate while using bleach
    3. Mix no more than one cup of bleach in one gallon of water
    4. Wash (scrub if necessary) item or surface with solution
    5. Rinse with clean water
    6. Dry surface so that it does not remain wet

    Bathroom Aerosols

    Flushing the toilet is known to produce aerosols that are capable of causing surface contamination within the toilet and bathroom.Many enteric pathogens are spread by the fecal-oral transmission route, and it
    has been suggested that droplets containing fecal matter, after toilet flushing,
    is an infection hazard, particularly during acute diarrheal illnesses.

    In one particular study of bacterial counts after toilet flushing…

    1. The most bacteria was found on the toilet seat.
    2. Closing the toilet lid had little effect in reducing the number of bacteria released into the air due to gaps between the top of the porcelain rim and the seat.  There is also a gap between the seat and the lid allowing aerosols to
      escape into the room.
    3. Another heavily colonized area was the recess under the rim of the toilet where limescale often accumulates, which aids in bacterial retention.
    4. Surface contamination in various locations around the toilet (as far as 83 cm away) was also detected thirty minutes after flushing.
    5. Direct transfer of microbes can easily take place due to aerosol
      contamination of bathroom surfaces.

    Bathroom items

    Toothbrushes are typically stored in a common container of a family bathroom.This provides a moist and humid environment which encourages bacterial growth. Contamination can occur from aerosols as a result of toilet flushing, poor hand hygiene and natural contaminants of the mouth that grow out to large numbers -they should be stored upright, uncovered, and in a non-humid environment to prevent bacterial proliferation.

    Contact lenses on the cornea can prevent oxygen and ionic diffusion and cause superficial alterations to the epithelial layer of the eye, which may make the cornea susceptible to microbial attachment and infection.

    1. Microbes commonly found on bathroom surfaces and in tap water (Pseudomonas aeruginosa, Candida albicans, Acanthamoeba, Fusarium, and Aspergillus) can contaminate contact lens storage cases, creating a risk for infection.
    2. Contact lens wearers should strictly comply with protocols of disinfection and cleaning that is recommended
    3. Fresh sterile solutions every time lenses are taken out
    4. Never tap water
    5. Avoid bathroom for lens hygiene regime
    6. Lens case cleaned each week (mild detergent and soft brush, following by saline rinse, left out to air dry
    7. Case replaced each month

    Cosmetics and toiletries are exposed to contamination due to their presence in
    the bathroom’s warm, moist environment. Examples of contamination:

    1. Fingers dipped into products
    2. Spillage of water into shampoos or shower preparations
    3. Swigging from bottles of mouthwash

    The eye is at risk for infection, in particular, from contaminated cosmetic applicators.


    Microorganisms in the Kitchen

    In one study, 76.6% of respondents reported that they believed household members were more likely to pick up germs outside of the household. The following may change your mind about where you think the germs are……

    Reservoirs/High risk areas

    1. Wet surfaces
    2. U-tubes
    3. Sinks
    4. Cutting boards
    5. Cleaning cloths/mops
    6. Sponges
    7. Countertops
    8. Faucet/drawer/door handles

    Since plain soap and water does not necessarily kill microorganisms, soap and water cleaning of contaminated surfaces and hands may actually spread microbial contamination in the environment

    Powered cooking equipment, like an electric blender, can lead to distribution of pathogens up to a 3-4 meter radius.

    In a study by Enriquez et al., pseudomonas and salmonella were most commonly isolated from sponges and cleaning cloths.

    Food Preparation

    • Approximately 76 million Americans develop food poisoning each year, and about 20% of reported foodborne illnesses occur in the home.
    • In a study of an outbreak of diarrhea caused by E. coli O157 in New Jersey, 80% of contaminated hamburgers were consumed in the home.
    • Ninety percent of salmonella infections are thought to be associated with the home environment.
    • Poultry meat is internationally recognized as an important vehicle of Campylobacter, especially when undercooked. Cross contamination is an important contributing factor in outbreaks on countertops, cutting boards, utensils, hands, etc.
    • J. Rayner et al. studied raw fruits and vegetables and their presence of microorganisms and biofilms.
      * Tomatoes – bacterial colonization and biofilm formation
      * Carrots – biofilms and fungal colonization. Bagged carrots had higher density of bacterial colonization than loose
      * Mushrooms – considerable amounts of biofilm on upper cap and in gill area


    • Food prep guidelines Certain raw foods or ingredients have a high risk of contamination such as meats, fish, poultry and eggs. Other foods may have a medium risk of contamination such as certain vegetables, which may have been contaminated during production, or which are soiled.
    1. A chopping board should be used for preparation of high-risk raw foods likely to be contaminated. After preparation of high-risk raw foods all surfaces which have come into contact with the food should be immediately decontaminated
    2. It is recommended that separate chopping boards should be used for raw meat and fish, for fresh fruit and vegetables and for other items.
    3. Hands must be washed immediately after handling raw food. It is important to be aware that, during and after handling high-risk raw food, any surface subsequently touched with the hands (even tap handles, refrigerator doors and cooker control knobs) will be contaminated with microorganisms from the food.
    4. Dish cloths and hand cloths used during the preparation of raw food must be decontaminated and dried. The use of disposable cloths/paper towels is recommended.
    5. After decontamination, cloths should be dried as rapidly as possible. If cloths are left in a damp condition residual contamination not destroyed by the decontamination process can rapidly multiply at ambient temperatures.

    Kitchen Water

    Because washing up removes organic matter from soiled items during food prep and consumption, it is one of the main control points for preventing the transmission of bacteria in the domestic kitchen.
    Temperature of water used for “washing up” can influence microbial survival. Most hand washed dishes use water temperatures below 50 C or lower, which is not high enough to destroy most organisms.
    In comparing washing up water temperature in a hospice with that in a domestic kitchen, the hospice water was consistently high while the bacterial count was consistently low compared to the domestic homes.
    The bottom line: don’t let your guard down at home!

    Microorganisms associated with laundry

    Risks associated with laundering

    Most people think that washed laundry is clean laundry, right? Researchers find that handling “clean” laundry presents a risk of exposure to potentially harmful microbes. Many studies have demonstrated that fabric and cloth can easily become contaminated with high level of microorganisms that can survive for long periods of time in fabrics.

    • People hang their clothing outside to dry (where sunlight can aid in denaturing microbes) much less frequently. Additionally, ironing, which could allow steam to reduce the microbial load on fabrics, is less common.
    • Of the 100-500 grams of feces excreted per day by the average America, it has been estimated that approximately 0.1 gram of residual fecal matter remains on the undergarment of any person
    • The consumer may believe that normal laundering produces clean clothes; however, this does not necessarily translate to bacteriologically clean due to detergents having a wide range of efficacy in reducing the bacteria contaminated on clothing.
    • Bacteria survive and grow in damp objects, such as contaminated cloths (much like laundry).
      * Common bacteria found in high numbers on a dish cloth are Shigella and E. coli O157:H7.
      * In one study, the numbers were high enough to be considered infectious doses and could easily be transferred to the lip or mouth having potential to cause disease.
    • Because home machines use water at temperatures of 25-60oC, the water is less effective at killing microbes. Washing machines are contaminated after use and can spread bacteria, such as Staphylococcus aureus (a common cause of skin infections), from previous loads to future loads of laundry.
    • Viruses, in general, are more resistant to disinfection by chlorination and detergents than bacteria.
           * In one study, the transfer of viruses to sterile cloth swatches in the laundry was very efficient for all viruses tested [adenovirus (pink eye, diarrhea), hepatitis A virus (hepatitis), and rotavirus (diarrhea)].
           * A sufficient number of rotavirus and hepatitis A virus survived in laundry washed only with detergent.
           * The most important steps in the reduction of viruses were the addition of bleach and drying in an automatic dryer.

    Laundry hygiene guideline

    Clothing, bed linens, towels and other items which are in constant or intermittent contact with the body may form an important route of transmission of microbial infections.

    Effective infection control practices with laundry include:

    1. Fabrics contaminated with microorganisms are most effectively decontaminated using soap/detergent and hot water washing (60°C).
    2. During laundering, the use of modern cleaning products effectively removes substrates from soiled fabrics which may support the growth of microorganisms.
    3. If lower temperature washes are used (<45°C), the addition of hypochlorite bleach is necessary for effective decontamination.
    4. Laundering of cloths, towels etc. which are used in association with food preparation should be done separately from laundering of clothes and bed linens.
    5. Handwashing after contact with soiled laundry.

    It is important to remember that relying on water temperatures to achieve bacterial and viral reductions may be impractical in the U.S. since water heaters are usually not set as high as the recommended temperature for effective sanitizing.

    Use of bleach or other targeted disinfectants/sanitizers, such as silver ions, is necessary to reduce contamination of washing machines. Even when used as a weekly “mouthwash” for the washing machine, bleach will help to keep the germ count down.



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