collected from subjects and follow-up stool cultures were requested 5–7 months later from individuals who were culture positive. Family members of culture-positive individu- als also provided stool samples to be exam- ined for colonization. A study conducted in the UK looked at the potential of pets as a reservoir of C. dif- ficile (Borriello et al., 1983). Fecal samples from dogs ( n = 52) and cats ( n = 20) were forwarded to researchers from veterinary hos- pitals and from colleagues to determine the prevalence of colonization with C. dicile . The earliest reported study that estimated the prevalence of C. dicile in the house- hold environment was published in 1981 in the U.S. (Kim et al., 1981). This study was conducted after the index case in an outbreak of C. dicile in a newborn intensive care unit experienced a recurrence of CDI after discharge home. The investigators collected samples from the bathroom (floor [ n = 15], sink cabinets [ n = 15], and inside toilet seat cover [ n = 10]); bedrooms (floor [ n = 15], bookcase [ n = 4], linens [ n = 10], and toys [ n = 15]); living room (crib [ n = 10]); utility room (floor [ n = 10], freezer door [ n = 5], and soiled clothing [ n = 10]); soil in yard ( n = 2); and tap water ( n = 2). Samples were also col- lected from a control home. A study conducted in Houston, Texas, examined 30 single family dwellings (Alam et al., 2014). Researchers collected 3–5 samples from each household. A total of 127 environmental samples from shoes ( n = 63), bathrooms ( n = 15), other household surfaces ( n = 37), and dust ( n = 12) were analyzed to determine prevalence of C. dicile in the household environment. Another study also conducted in Hous- ton, Texas, involved examining the soles of shoes ( n = 280), doorsteps ( n = 186), cleaning supplies ( n = 189), kitchens ( n = 191), and restrooms ( n = 189) in a convenience sample of 1,079 households over a 2-year period (2013–2015) to estimate prevalence of C. dif- ficile in the household environment (Alam et al., 2017). A study conducted in the U.S. reported the examination of 35 rural and urban house- holds to estimate the prevalence of C. di- cile in the environment (Rodriguez-Palacios et al., 2017). A total of 467 samples of food (collected from 188 kitchen pots or refrig- erators [no other detail provided]) and 278
samples of environmental surfaces (kitchen countertops [ n = 32], sinks [ n = 56], refrig- erator shelves [ n = 59], gloves [ n = 23], shoes [ n = 56], and washing machines [ n = 52]) were collected. One study in Slovenia of urban and rural households that had a dog involved sampling shoes, slippers, and dog paws to estimate the prevalence of C. dicile in the household environment (Janezic et al., 2018). In total, 20 households provided a total of 90 samples collected from dog paws ( n = 25), shoes ( n = 44), and slippers ( n = 21). Another study estimated prevalence of C. dicile in the outdoor household envi- ronment (Janezic et al., 2020). Researchers examined outdoor sites in the gardens of five households in Slovenia: four were rural households and one was from a suburban area. A total of five samples were taken at each house: three from the compost pile, one from the flower garden, and one from the vegetable garden. A study conducted in Southwestern Ontario, Canada, to estimate the prevalence of C. dicile involved collection of environ- mental samples from 9 locations in each of 84 households in a convenience sample of households that had a dog (Weese et al., 2010). The sample locations were the kitchen sink and tap ( n = 84), refrigerator shelf ( n = 84), toilet ( n = 83), kitchen counter ( n = 84), vacuum cleaner contents ( n = 81), and any pet food bowls ( n = 84). The study also assessed colonization of dogs ( n = 139) and cats ( n = 14) from these households. Case-Control Studies A study published in the U.S. used records of military dependents receiving healthcare to evaluate risk factors related to community- associated CDI, including exposure to a fam- ily member with CDI (Adams et al., 2017). Cases were identified as those with diagnostic codes for CDI and were matched on age and sex with three controls (i.e., individuals with- out diagnosis codes for CDI). A second study published in the U.S. evalu- ated risk factors for young children acquir- ing CDI (Weng et al., 2019). C. dicile cases were identified via the Emerging Infections Program of the Centers for Disease Control and Prevention. Controls were randomly chosen from a commercial database of tele- phone numbers or from birth registries; con-
trols resided in the same surveillance catch- ment area. Exposure to household members who had CDI, diarrhea, or wore diapers was evaluated, as were various foods (including eggs, dairy, raw vegetables, plant-based pro- tein, red meat, poultry, seafood, and well or spring water) as potential risk factors for CDI. A third study in the U.S. was conducted with patients who were CDI positive ( n = 435) and CDI negative ( n = 461) (Berinstein et al., 2021). Cases and controls were identi- fied using electronic medical records and then verified by manual chart review. An electronic survey was administered to assess household exposures to pets as well as intake of meat, dairy, and salad as potential risk factors. Case Series Studies A case series report published as an edito- rial in the UK reported results of a study conducted to determine the presence of CDI. The researchers searched a database of microbiological reports to identify cases of CDI with the same address or surname as a case (Baishnab et al., 2013). Individuals who appeared to live in the same household as a case were contacted for further investigation into their experiences related to CDI. A case series study conducted in the U.S. involved telephone interviews with commu- nity-associated CDI cases ( n = 984) to ask about frequency of exposure to household members with CDI, exposure to household pets, and consumption of food (i.e., chicken, beef, pork, lamb) during a typical week (Chitnis et al., 2013). Cases were classified into one of three levels of exposure based on the information provided in the inter- view. Stool samples were also collected from a convenience sample (40%) of the inter- viewed patients. The samples were cultured for C. dicile . Cross-Sectional Studies A study published in the U.S. to assess risk of transmission within family contacts included individuals from households with two or more members enrolled in the same health insurance plan (Miller et al., 2020). Cases of CDI were identified using diagnostic codes. Individuals were assigned to one of four groups based on their exposure to a family member (i.e., family member with CDI diag- nosis in the prior 60 days or not) and their CDI status (i.e., positive or negative).
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