Staff Fingernails Implicated in Pseudomonas Outbreak

Abstract & Commentary

Synopsis: Evidence supported a possible relationship between long or artificial fingernails in the colonization of health care workers’ hands and a prolonged outbreak of Pseudomonas aeruginosa in a neonatal ICU.

Source: Moolenaar RL, et al. Infect Control Hosp Epidemiol 2000;21:80-85.

This study was initiated when 34 patients in a neonatal ICU (NICU) developed a bloodstream infection or endotracheal tube (ETT) colonization with Pseudomonas aeruginosa, resulting in 11 deaths. The process of investigation involved: 1) computing attack and case-fatality rates for the period of the outbreak; 2) cultures of potential environmental sources (ventilator equipment, sink drains, faucets, hand lotion, cleaning agents) and the hands and external ear canals of 104 unit staff (nurses, physicians, nurse practitioners, respiratory therapists, clerical and housekeeping staff) on an unscheduled basis; 3) genotyping all available P. aeruginosa isolates from stored specimens (ETT, blood, wound) and the environmental survey; and 4) a case-control study.

A case-patient was defined as an infant from whom P. aeruginosa was isolated from the blood or ETT within 14 days of NICU admission. Controls were randomly selected from the NICU admission log and matched with case-patients based on birth weight. To be considered a control, the infant had to be admitted to the NICU during the same time as the case-patients and hospitalized in the NICU for 14 days or longer. The ratio of controls per case was 2:1.

Of the 519 infants admitted to the NICU during the study period, 46 met the case definition, resulting in an attack rate of 10.5%. P. aeruginosa was isolated from two sink drains and several other areas in the hospital; however, these isolates were a distinct genotype unrelated to any of the human specimens. Of the 104 health care workers, three nurses had P. aeruginosa isolated from their hands. Two (Nurse A1 and Nurse A2) were positive for genotype A. A third (Nurse B) was positive for genotype B. Most case-patients also had genotype A (75%) or B (15%). Nurse A1 had long natural fingernails, Nurse B had long artificial fingernails, and Nurse A2 had short, natural fingernails.

Case-patients were more likely than controls to have Nurse A1 or Nurse B provide care during the exposure period, after adjusting for birth-weight category (odds ratio [OR], 11.4; CI95, 3.3-40.0; P = 0.0001; and OR, 3.6; CI95, 1.3-9.7; P = 0.01). The number of ventilator days during the exposure period, and hours exposed to nurses with long natural fingernails, were also factors associated with being a case-patient. No other exposure to a health care worker, including Nurse A2, was associated with being a case-patient. When all significant variables were entered into a multivariate model, only exposure to Nurse A1 (OR, 10.37; CI95, 2.86-37.58; P < 0.001) or Nurse B (OR, 3.08; CI95, 1.02-9.32; P < 0.05) remained as independent risk factors for acquiring colonization of infection with P. aeruginosa within the first 14 days of NICU admission.

During the survey period, a policy was introduced that restricted use of artificial fingernails and limited nail length to short or medium. The importance of infection control measures (e.g., careful hand washing and glove use) was emphasized. Afterward, ETT colonization persisted, but no P. aeruginosa bloodstream infections were reported for three months. However, they recurred in the fourth month after the policy change and educational intervention.


The major finding of this study was the statistically significant association between colonization or infection with P. aeruginosa and contact with two specific nurses who had P. aeruginosa isolated from their hands. The evidence linking the two nurses to the outbreak included: 1) microbiological evidence—culture of their hands yielded the epidemic organism; 2) genetic evidence—the isolates recovered from the nurses’ fingertips were identical by pulsed-field electrophoresis; and 3) epidemiological evidence—case-control analysis demonstrated a significant association between exposure to these two nurses and acquiring P. aeruginosa.

The association was deemed sufficiently strong in this Oklahoma City hospital to implement a new policy restricting nurses in the NICU from wearing long (either natural or artificial) fingernails as an infection control measure. Concurrently, an educational program was provided that stressed the importance of hand washing and glove use. The policy was initially effective (0 cases for 3 months); however, the problem recurred in the fourth month.

Because the institution implemented the nail length policy and educational program at the same time, it is impossible to determine whether one or both was responsible for the diminished number of cases. Most likely, the solution was multifactorial, given that the incidence of P. aeruginosa declined to zero for the three months after the policy and the educational program were introduced and then relapsed.

There are several limitations to this study. The mechanism by which the nurses initially became contaminated was not identified. Their hand contamination may have been the cause or the result of the outbreak. Hand-washing practices were not observed, so it is not known if these individuals’ practices differed from other health care workers. All health care workers with long or artificial nails did not have positive cultures. Accordingly, findings of this study suggest, but do not prove, that the presence of long or artificial fingernails may play a role in the transmission of infection. Further study is needed to better define the problem. In the interim, short natural nails are a reasonable choice that may reduce the risk for hospital-acquired infection. (Leslie Hoffman is Professor, Medical-Surgical Nursing Chair, Department of Acute/Tertiary Care, University of Pittsburgh School of Nursing, Pittsburgh, Penn.)

(Editor’s note: See also Passaro DJ, et al. J Infect Dis 1997;175:992-995; and Deresinski SC. Infect Dis Alert 1997;22:173.)