Cross-contamination and infection in the domestic environment and the role of chemical disinfectants

Food safety knowledge of consumers and the microbiological and temperature status of their refrigerators

The objectives of this study were to examine domestic food safety knowledge levels of consumers, establish the levels and incidence of bacterial contamination and operational temperatures in domestic refrigerators, and identify areas in which consumer food safety education is necessary in Ireland. A food safety knowledge questionnaire applied to a representative sample of households (n = 1,020) throughout the island of Ireland found the gaps in consumer food safety knowledge. Analysis of swab samples (n = 900) recovered from the domestic refrigerators in these households showed average total viable counts of 7.1 log CFU/cm2 and average total coliform counts of 4.0 log CFU/cm2. Analysis of swab samples also detected the incidence of Staphylococcus aureus (41%), Escherichia coli (6%), Salmonella enterica (7%), Listeria monocytogenes (6%), and Yersinia enterocolitica (2%). Campylobacter jejuni and E. coli O157:H7 were not detected in domestic refrigerators. The temperature profiles of a subset of the sampled refrigerators (100) were monitored for 72 h, and 59% were found to operate, on average, at temperatures above the recommended 5 degrees C. Knowledge and temperature survey results varied considerably, but consumers who scored better in terms of basic food safety knowledge had reduced levels of bacterial contamination in their refrigerators and reported a reduced incidence of food-associated illnesses. This study confirms the effect of basic food hygiene knowledge on hygienic practice and identifies specific areasfor emphasis in the development and delivery of effective food safety risk communication messages to consumers.

Occurrence of bacteria and biochemical markers on public surfaces

From 1999-2003, the hygiene of 1061 environmental surfaces from shopping, daycare, and office environments, personal items, and miscellaneous activities (i.e., gymnasiums, airports, movie theaters, restaurants, etc.), in four US cities, was monitored. Samples were analyzed for fecal and total coliform bacteria, protein, and biochemical markers. Biochemical markers, i.e., hemoglobin (blood marker), amylase (mucus, saliva, sweat, and urine marker), and urea (urine and sweat marker) were detected on 3% (26/801); 15% (120/801), and 6% (48/801) of the surfaces, respectively. Protein (general hygiene marker) levels > or = 200 microg/10 cm2 were present on 26% (200/801) of the surfaces tested. Surfaces from children's playground equipment and daycare centers were the most frequently contaminated (biochemical markers on 36%; 15/42 and 46%; 25/54, respectively). Surfaces from the shopping, miscellaneous activities, and office environments were positive for biochemical markers with a frequency of 21% (69/333), 21% (66/308), and 11% (12/105), respectively). Sixty samples were analyzed for biochemical markers and bacteria. Total and fecal coliforms were detected on 20% (12/60) and 7% (4/ 60) of the surfaces, respectively. Half and one-third of the sites positive for biochemical markers were also positive for total and fecal coliforms, respectively. Artificial contamination of public surfaces with an invisible fluorescent tracer showed that contamination from outside surfaces was transferred to 86% (30/ 35) of exposed individual's hands and 82% (29/35) tracked the tracer to their home or personal belongings hours later. Results provide information on the relative hygiene of commonly encountered public surfaces and aid in the identification of priority environments where contaminant occurrence and risk of exposure may be greatest. Children's playground equipment is identified as a priority surface for additional research on the occurrence of and potential exposure to infectious disease causing agents.

Transfer of Salmonella and Campylobacter from stainless steel to romaine lettuce

The degree of transfer of Campylobacter jejuni and Salmonella enterica serovar Typhimurium was evaluated from a stainless steel contact surface to a ready-to-eat food (lettuce). Stainless steel coupons (25 cm2) were inoculated with a 20-microl drop of either C. jejuni or Salmonella Typhimurium to provide an inoculum level of approximately 10(6) CFU/28 mm2. Wet and dry lettuce (Lactuca sativa var. longifolia) pieces (9 cm2) were placed onto the inoculated stainless steel surface for 10 s after the designated inoculum drying time (0 to 80 min for C. jejuni; 0 to 120 min for Salmonella Typhimurium), which was followed by the recovery and enumeration of transferred pathogens (lettuce) and residual surface pathogens (stainless steel coupons). For transfers of Salmonella Typhimurium to dry lettuce, there was an increase from 36 to 66% in the percent transfer of the initial inoculum load during the first 60 min of sampling and then a precipitous drop from 66 to 6% in percent transfer. The transfer of Salmonella Typhimurium to wet lettuce ranged from 23 to 31%, with no statistically significant difference between recoveries over the entire 120-min sampling period. For C. jejuni, the mean percent transfer ranged from 16 to 38% for dry lettuce and from 15 to 27% for wet lettuce during the 80-min sampling period. The results of this study indicate that relatively high numbers of bacteria may be transferred to a food even 1 to 2 h after surface contamination. These findings can be used to support future projects aimed at estimating the degree of risk associated with poor handling practices of ready-to-eat foods.

Developing an effective policy for home hygiene: a risk-based approach

Evaluation of the infection potential in the home suggests that improved hygiene practice could significantly reduce the impact of infectious diseases. Fundamental to developing infection prevention policy for the home is the need to recognise that people live in an environment where all human activities occur, including food and water hygiene, hand hygiene, and hygiene related to care of vulnerable groups. In all these situations, reducing infection risks is based on the same underlying microbiological principles. In developing countries, disposal of human and animal excreta and other waste is often also the responsibility of the family and community. Adopting a holistic approach provides the opportunity for a rational approach to home hygiene based on risk assessment. The International Scientific Forum on Home Hygiene (IFH) believes that to deliver hygiene policy with real health benefits, a risk-based approach must be developed and promoted for the home. A risk-based approach starts from the principle that pathogens are introduced continually into homes on people, food and water, pets, insects and air. Inadequate disposal of human and animal excreta serves to increase this risk. Additionally, sites where stagnant water accumulates, such as sinks, toilets and cleaning cloths can support microbial growth and become a source of infection. By assessing the frequency occurrence of pathogens and potential pathogens on hands, hand and food contact surfaces, laundry, reservoir and reservoir/disseminator sites, together with the potential for transfer in the home, the exposure risk can be assessed.

Hygiene measures considering actual distributions of microorganisms in Japanese households

AIMS

Effective household hygiene measures require that sources of bacterial contamination and the places to which contamination spreads be carefully identified. Therefore, a study was performed to examine the distribution of microorganisms throughout ordinary households in Japan, which has its own unique customs of daily life and food preparation.

METHODS AND RESULTS

Using the stamping method, samples were taken from 100 different places and items in each of 86 households. This study found kitchens/dining rooms to have the greatest level of microbial contamination and bathrooms, the next highest level. Toilets (water closets) were found to have an unexpectedly low level of bacterial contamination. The largest bacterial counts were found on items such as drain traps, dish-washing sponges, counter towels, sinks, dish-washing tubs, and bathroom sponges.

CONCLUSIONS

It is necessary to carefully identify both the items that can become instruments for spreading bacterial contamination and the places that easily become subject to secondary contamination, and then to take timely and effective disinfection/sanitizing measures.

SIGNIFICANCE AND IMPACT OF THE STUDY

The data gathered in this study will be very valuable for anticipating the pathways over which bacteria are transported and prioritizing disinfection targets, to make effective disinfection possible.

Home hygiene: a risk approach

The need to place "prevention through hygiene" at the core of strategies for infection prevention has been emphasised by recent events. Indications are that re-evaluation of current practice and the promotion of improved hygiene in the domestic setting could have a significant impact in reducing infectious disease. If the public are to play a part however they must be properly informed. Encouraging the concept of the home as a setting in which the whole range of activities occur, including food hygiene, personal hygiene and hygiene related to medical care, provides the opportunity for a rational approach to home hygiene based on risk assessment. In the home surfaces (including hand surfaces) and other sites play an important part in the transmission of infection, especially food-borne infections. From an assessment of the frequency of occurrence of pathogens and potential pathogens at reservoirs, disseminators and hand and food contact sites together with the potential for transfer within the home, the risks of exposure can be assessed. This can be used to develop a rational approach in which effective hygiene procedures involving cleaning and disinfection as appropriate are targeted at these sites to reduce risks of cross contamination. This approach is consistent with the view that good home hygiene is not about "getting rid of household germs" but about targeting hygiene measures appropriately to reduce exposure to germs and thereby prevent cross infection. In motivating change, education programmes must take account of concerns related to antimicrobial resistance, the environment and the "health" of the immune system.

Achieving hygiene in the domestic kitchen: the effectiveness of commonly used cleaning procedures

AIMS

To quantify the transmission of Salmonella and Campylobacter to hands, cloths, and hand- and food-contact surfaces during the preparation of raw poultry in domestic kitchens, and to examine the impact on numbers of these bacteria of detergent-based cleaning alone, or in conjunction with thorough rising.

METHODS AND RESULTS

Groups of volunteers prepared chickens for cooking. Surfaces were sampled either before cleaning or after cleaning using water and detergent with or without thorough rinsing. Although cleaning followed by rinsing consistently achieved decontamination of surfaces contaminated with Campylobacter, significant numbers of surfaces were still contaminated with low numbers of Salmonella. Where cloths contaminated with Salmonella were stored overnight, a reduction in the efficacy of detergent-based cleaning regimes was observed.

CONCLUSIONS

Rinsing is the critical step in ensuring that bacteria are removed from surfaces during cleaning, but this may still leave residual contamination. Growth of Salmonella occurs in some contaminated cloths during overnight storage; Salmonella on cloths stored overnight are also more difficult to remove by washing.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rinsing, as part of the cleaning process, is a critical step in achieving hygiene in the kitchen. However, to achieve completely hygienic surfaces, the use of an antimicrobial agent may be necessary.

Bacterial contamination of Japanese households and related concern about sanitation

The bacterial contamination of Japanese homes and the attitudes of Japanese people toward sanitation were studied. By taking bacterial counts of approximately 90 places each in five homes, this study found kitchens to have the greatest degree of bacterial contamination, followed by bathing rooms. Toilets had less bacterial contamination than was expected. While concern about bacteria on highly contaminated items such as sponges, towels for wiping counters, and other reservoirs/disseminators was common, there was a relative lack of concern regarding contact surfaces such as dining tables. It is believed that an in-depth study of bacterial contamination in the home and concern about it would lead to the promotion of greater public understanding of home sanitation and help to facilitate the provision of useful information and products to the public.

Effects of antibacterial dishwashing liquid on foodborne pathogens and competitive microorganisms in kitchen sponges

In response to increasing concern about home hygiene, the use of antibacterial products to reduce microorganisms in kitchen sponges and cleaning cloths is strongly promoted by some producers of detergent for domestic use. The effects of an antibacterial dishwashing liquid on Escherichia coli, Salmonella Enteritidis, Staphylococcus aureus, and Bacillus cereus were investigated in a modified suspension test and in used sponges with and without food residues under laboratory conditions. A limited study was conducted in households to assess the efficacy of antibacterial dishwashing liquid as used by the consumer. In the suspension tests, S. aureus and B. cereus were shown to be susceptible to low concentrations of antibacterial dishwashing liquid (0.5%), whereas E. coli and Salmonella Enteritidis maintained their initial numbers for at least 24 h at 25 degrees C. At higher concentrations (2 to 4%), all test organisms decreased to below the detection limit after 24 h. Over a 24-h period, the antibacterial dishwashing liquid did not significantly reduce these organisms in used sponges in which food residues were present. The antibacterial product did not reduce the competitive microorganisms either. Similar results were found for sponges involved in daily household use. The results of this study demonstrate that the antibacterial dishwashing liquid was effective in reducing pathogens in the suspension test but not in the used sponges. This finding indicates that to determine the efficacy of antibacterial products, their use in a household setting must be considered.

The role of the home environment in the transmission of infectious diseases

The purpose of this paper is to examine current health care literature (1980-2000) regarding the microbiology of the home environment, to summarize evidence of transmission within the home, and to assess effectiveness of cleaning practices and products. The home environment, particularly the kitchen and bathroom, serves as a reservoir of large numbers of microorganisms, particularly Enterobacteriacae, and infectious disease transmission has been demonstrated to occur in 6-60% of households in which one member is ill. Current food preparation and cleaning practices provide multiple opportunities for intra-household member spread. Routine cleaning is often sufficient, but in cases of household infection, may not adequately reduce environmental contamination. The effectiveness of disinfectants varies considerably and depends on how they are used as well as their intrinsic efficacy. The behavioral aspects of infection prevention in the home (e.g., foodhandling and cleaning practices) warrant increased public attention and education.

The effect of interfering substances on the disinfection process: a mathematical model

AIMS

To gain a greater understanding of the effect of interfering substances on the efficacy of disinfection.

METHODS AND RESULTS

Current kinetic disinfection models were augmented by a term designed to quantify the deleterious effect of soils such as milk on the disinfection process of suspended organisms. The model was based on the assumption that inactivation by added soil occurred at a much faster rate than microbial inactivation. The new model, the fat-soil model, was also able to quantify the effect of changing the initial inoculum size (1 x 10(7)-5 x 10(7) ml(-1) of Staphylococcus aureus) on the outcome of the suspension tests. Addition of catalase to the disinfection of Escherichia coli by hydrogen peroxide, resulted in changes to the shape of the log survivor/time plots. These changes were modelled on the basis of changing biocide concentration commensurate with microbial inactivation.

CONCLUSIONS

The reduction in efficacy of a disinfectant in the presence of an interfering substance can be quantified through the use of adaptations to current disinfection models.

SIGNIFICANCE AND IMPACT OF THE STUDY

Understanding the effect of soil on disinfection efficacy allows us to understand the limitations of disinfectants and disinfection procedures. It also gives us a mechanism with which to investigate the soil tolerance of new biocides and formulations.

Observation of everyday hand-washing behavior of Japanese, and effects of antibacterial soap

People wash their hands only for a short time outside the home and when preparing meals at home. This may not be sufficient for those who prepare meals because of possible secondary contamination from food. Although washing with a placebo soap for a short period (lathering 3 s and rinsing 8 s) cleansed from hands about 95% of the total coliforms transferred from ground meat, an antibacterial soap further reduced the coliform count significantly (p < 0.01). To effectively avoid secondary contamination, it is recommended that people should more frequently wash their hands, using an antibacterial soap on the areas that have been in contact with raw meat, poultry, seafood, eggs, vegetables and other foods.

Home hygiene practices and infectious disease symptoms among household members

Public health programs are generally targeted to communitywide, population-based prevention strategies, with little attention focused on the home environment as one potential source of transmission of infectious diseases. The purpose of this correlational prevalence survey was to describe the relationship between home hygiene practices and prevalence of infectious disease symptoms among household members. Three hundred and ninety-eight households with 1,662 members in an inner-city population (96.4% Hispanic) were surveyed to examine hygiene practices and determine the presence of transmission of infection, defined as the presence of the same symptom(s) in two or more household members for which at least one individual sought medical attention and received treatment. At least one individual in 78.6% of households reported symptoms of infection in the previous 30 days, and 37.9% of households met the definition of disease transmission. In univariate analyses, five factors were significantly associated with risk of household transmission, but in the logistic regression model, only use of communal laundry (p = 0.009) and lack of bleach use (p = 0.04) were significantly predictive of increased risk of transmission. This is the first comprehensive survey of home hygiene practices and the first study to identify a potential link between laundry and risk of disease transmission in homes. This potential link warrants further study in clinical trials.

Quantification and variability analysis of bacterial cross-contamination rates in common food service tasks

This study investigated bacterial transfer rates between hands and other common surfaces involved in food preparation in the kitchen. Nalidixic acid-resistant Enterobacter aerogenes B199A was used as a surrogate microorganism to follow the cross-contamination events. Samples from at least 30 different participants were collected to determine the statistical distribution of each cross-contamination rate and to quantify the natural variability associated with that rate. The transfer rates among hands, foods, and kitchen surfaces were highly variable, being as low as 0.0005% and as high as 100%. A normal distribution was used to describe the variability in the logarithm of the transfer rates. The mean +/- SD of the normal distributions were, in log percent transfer rate, chicken to hand (0.94 +/- 0.68), cutting board to lettuce (0.90 +/- 0.59), spigot to hand (0.36 +/- 0.90), hand to lettuce (-0.12 +/- 1.07), prewashed hand to postwashed hand (i.e., hand washing efficiency) (-0.20 +/- 1.42), and hand to spigot (-0.80 +/- 1.09). Quantifying the cross-contamination risk associated with various steps in the food preparation process can provide a scientific basis for risk management efforts in both home and food service kitchens.

Epidemiological relationships between Aeromonas strains isolated from symptomatic children and household environments as determined by ribotyping

Ribotyping was used to study the epidemiology of Aeromonas associated gastro-enteritis in young children. Ribotyping patterns of 29 Aeromonas strains (16 Aeromonas caviae, 8 Aeromonas hydrophila, 3 Aeromonas eucrenophila, 1 Aeromonas veronii, and 1 Aeromonas encheleia) isolated from primary stool cultures of sick children were compared using the GelCompare software with patterns of 104 strains (39 Aeromonas eucrenophila, 29 Aeromonas caviae, 11 Aeromonas encheleia, 10 Aeromonas hydrophila, 6 Aeromonas bestiarum, 3 Aeromonas veronii, 3 Aeromonas popoffii and 3 Aeromonas media) isolated from their household environment in order to investigate the route of transmission of these bacteria. Fifteen strains (approximately 47%) isolated from stool cultures of patients showed the same riboprofile as strains found in contacts or environment. In particular, three strains isolated from patients shared the same riboprofile with strains found in their domestic environment. The wide diffusion of potentially pathogenic Aeromonas strains in our household samples, and the high rate of asymptomatic carriers among family members, suggested that predisposing factors of the host could make children prone to an Aeromonas-related intestinal disease.

[Microbiological conditions of hospital beds before and after terminal cleaning]

INTRODUCTION

The hospital's environment keeps a close relationship with hospital infection, which may promote focus of contact and transmission. The terminal cleaning of patient unit represents one way to control microbiological environmental contamination. The study has as its main objective to evaluate the microbiological conditions of hospital mattresses before and after cleaning.

METHODS

Rodac plates were utilized for specimen collection with culture medium - blood agar plate. The patients beds were chosen by criteria established before hand and the places for specimen collection in the mattress were chosen by aleatory drawing. To the study of numerical alteration related to the positivity of plates before and after cleaning, Goodman' statistics tests were used.

RESULTS

From 52 mattress investigated, 520 culture plates were done from which 514 (98,8%) had a positive culture, 259 before cleaning and 255 after cleaning showing a reduction of positive cultures in only 4 plates after cleaning.

CONCLUSIONS

The number of plates with countable and countless colonies suggests that the cleaning, as it is done, instead of reducing the microorganism is dislocating it to other areas of the mattress keeping the microbiological condition as it was before the cleaning process.