In-use tests.
The effect of a social hand wash “in real life” has also been studied. Among 224 healthy homemakers, a single hand wash had little impact on microbial counts (mean log counts before hand wash, 5.72 ± 0.99; mean log counts after hand wash, 5.69 ± 1.04) (
307). In a study with 11 volunteers who washed their hands for 15 s with water alone 24 times per day for a total of 5 days, a slight increase of the bacterial counts was observed (mean log bacterial counts: prewash, 4.91 ± 0.46; postwash, 5.12 ± 0.44); when bar soap was used, a similar result was found (mean log bacterial counts: prewash, 4.81 ± 0.46; postwash, 5.07 ± 0.47) (
299). Other authors, too, have found paradoxical increases in bacterial counts on the skin after hand washing with plain soap (
299,
371,
611). In contrast, another study showed that a 5-min hand wash with regular bar soap reduced the resident hand flora by 0.33 log10 units (
326). The use of a nonmedicated soap by a surgical nurse for the preoperative treatment of hands even led to eight cases of surgical-site infection after cardiac surgery, which underscores the limited efficacy of nonmedicated soap (
226).
Some studies have examined only microorganisms that are left on the hands after a hand wash.
Washing hands with soap and water has been described to be ineffective in eliminating adenovirus from the culture-positive hands of a physician and patients, indicating that mechanical removal was incomplete (235). Transient gram-negative bacteria remained on the hands of health care workers in 10 of 10 cases despite five successive hand washes with soap and water (187). Furthermore, transmission of gram-negative bacteria from hands has been shown to occur 11 of 12 cases when a simple hand wash is carried out (129).