Development and evaluation of a record linkage protocol for Utah's Controlled Substance Database.

Utah's Controlled Substance Database prescription registry does not include master identifiers to link records for individual patients. We describe and evaluate a linkage protocol for Utah's Controlled Substance Database. Prescriptions (N = 22,401,506) dated 2005-2009 were linked using The Link King software and patient identifiers (e.g. names, dates of birth) for 2,232,725 patients. Review of 998 randomly selected record pairs classified 46 percent as definitely correct links and 54 percent as probably correct links. A correct link could not be confirmed for <1 percent. None were classified as probably incorrect links or definitely incorrect links. Record set reviews (N = 100 patients/set for 10 set sizes, randomly selected) classified 27-49 percent as definitely correct links and 39-63 percent as probably correct links. Fewer had too little information to confirm a link (5%-22%) or were probably incorrect (0%-6%). None were definitely incorrect. Overall, results suggest that Utah's Controlled Substance Database records were correctly linked. These data may be useful for cross-sectional and longitudinal studies of patient-controlled substance prescription histories.

Specialty of prescribers associated with prescription opioid fatalities in Utah, 2002-2010.

UNLABELLED: Opioid adverse events are widespread, and deaths have been directly attributed to opioids prescribed by medical professionals. Little information exists on the amount of opioids various medical specialties prescribe and the opioid fatality rate that would be expected if prescription opioid-related deaths were independent of medical specialty. OBJECTIVE: To compute the incidence of prescription opioid fatalities by medical specialty in Utah and to calculate the attributable risk (AR) of opioid fatality by medical specialty. DESIGN: Prevalence database study design linking the Utah Controlled Substance Database (CSD) for prescribing data with the Utah Medical Examiner data to identify prescription opioid fatalities. AR were calculated for each medical specialty and year. RESULTS: Opioid prescriptions are common with 23,302,892 recorded in the CSD for 2002-2010, 0.64% of which were associated with a fatality. We attached specialty to 90.2% of opioid prescriptions. Family medicine and internal medicine physicians wrote the largest proportion of prescriptions (24.1% and 10.8%) and were associated with the greatest number of prescription opioid fatalities. The number of active prescriptions at time of death decreased each year. The AR of fatality by provider specialty varied each year with some specialties, such as pain medicine and anesthesiology, consistently associated with more fatalities per 1,000 opioid prescriptions than internal medicine physicians the same year. CONCLUSIONS: Primary care providers were the most frequent prescribers and the most often associated with opioid fatalities and should be targeted for education about safe prescribing along with specialties that prescribe less frequently but are associated with a positive AR for opioid fatality.

Opioid prescribing knowledge and practices: provider survey following promulgation of guidelines-Utah, 2011.

OBJECTIVE: The Utah Department of Health published the Utah Clinical Guidelines on Prescribing Opioids for Treatment of Pain in 2010. The objective was to evaluate the impact of the Guidelines on provider behaviors such as documentation and use of screening tools. SETTING: Web-based questionnaire about opioid prescribing knowledge and practices distributed among 85 providers of a university-based, primary care community clinic system in the summer of 2011. MAIN OUTCOME MEASURES: Provider-reported knowledge about and comfort prescribing opioids and use of tools for managing opioid patients. RESULTS: Forty-seven providers who prescribe opioids on an outpatient basis completed the questionnaire after an initial e-mail invitation and two reminders (55 percent response rate). Providers most often used simple rating scales that can be included easily in the notes of the electronic medical record (EMR) to assess pain. When treating patients with chronic pain, 26 percent of respondents reported that they did not use any tool for patient assessment prior to treatment. Providers desire more training in opioid prescribing and feel that they lack referral resources for patients with chronic, noncancer pain. Prescription monitoring program use was common with 77 percent of providers reporting that they would access the system before prescribing opioids for a new patient. CONCLUSIONS: System-level changes such as inclusion of screening tools into EMRs will be needed to improve compliance with the Guidelines. Providers find treatment of chronic pain to be challenging and something for which they desire additional training and referral support.

"Blueprint version 2.0": updating public health surveillance for the 21st century.

Rapid changes to the United States public health system challenge the current strategic approach to surveillance. During 2011, the Council of State and Territorial Epidemiologists convened national experts to reassess public health surveillance in the United States and update surveillance strategies that were published in a 1996 report and endorsed by the Council of State and Territorial Epidemiologists. Although surveillance goals, historical influences, and most methods have not changed, surveillance is being transformed by 3 influences: public health information and preparedness as national security issues; new information technologies; and health care reform. Each offers opportunities for surveillance, but each also presents challenges that public health epidemiologists can best meet by rigorously applying surveillance evaluation concepts, engaging in national standardization activities driven by electronic technologies and health care reform, and ensuring an adequately trained epidemiology workforce.

Unintentional prescription opioid-related overdose deaths: description of decedents by next of kin or best contact, Utah, 2008-2009.

BACKGROUND: Little is known about the characteristics that may predispose an individual to being at risk for fatal overdose from prescription opioids. OBJECTIVE: To identify characteristics related to unintentional prescription opioid overdose deaths in Utah. DESIGN: Interviews were conducted (October 2008-October 2009) with a relative or friend most knowledgeable about the decedent's life. SUBJECTS: Analyses involved 254 decedents aged 18 or older, where cause of death included overdose on at least one prescription opioid. KEY RESULTS: Decedents were more likely to be middle-aged, Caucasian, non-Hispanic/Latino, less educated, not married, or reside in rural areas than the general adult population in Utah. In the year prior to death, 87.4 % were prescribed prescription pain medication. Reported potential misuse prescription pain medication in the year prior to their death was high (e.g., taken more often than prescribed [52.9 %], obtained from more than one doctor during the previous year [31.6 %], and used for reasons other than treating pain [29.8 %, almost half of which "to get high"]). Compared with the general population, decedents were more likely to experience financial problems, unemployment, physical disability, mental illness (primarily depression), and to smoke cigarettes, drink alcohol, and use illicit drugs. The primary source of prescription pain medication was from a healthcare provider (91.8 %), but other sources (not mutually exclusive) included: for free from a friend or relative (24 %); from someone without their knowledge (18.2 %); purchase from a friend, relative, or acquaintance (16.4 %); and purchase from a dealer (not a pharmacy) (11.6 %). CONCLUSIONS: The large majority of decedents were prescribed opioids for management of chronic pain and many exhibited behaviors indicative of prescribed medication misuse. Financial problems, unemployment, physical disability, depression, and substance use (including illegal drugs) were also common.

Risk factors for prescription opioid-related death, Utah, 2008-2009.

OBJECTIVE: Utah prescription opioid death rates increased nearly fivefold during 2000-2009. Inadequate understanding of risk factors hinders prevention. The goal of this study was to determine risk factors for prescription opioid death in Utah. DESIGN: Case-control study. Cases were 254 Utah decedents with ≥1 prescription opioid causing death during 2008-2009 with nonintentional manner of death (information obtained via next-of-kin interviews). Controls were 1,308 Utah 2008 Behavioral Risk Factor Surveillance System respondents who reported prescription opioid use during the previous year. OUTCOME MEASURES: Exposure prevalence ratios (EPRs) for selected characteristics and confidence intervals (CIs) were calculated. RESULTS: Decedents were more likely than the comparison group to have used prescription pain medication more than prescribed (52.9% vs 3.2%; EPR, 16.5; 95% CI, 9.3-23.7), obtained prescription pain medication from nonprescription sources (39.6% vs 8.3%; EPR, 4.8; 95% CI, 3.6-6.0), smoked daily (54.5% vs 9.7%; EPR, 5.6; 95% CI, 4.4-6.9), not graduated high school (18.5% vs 6.2%; EPR, 3.0; 95% CI, 2.0-3.9), and been divorced or separated (34.6% vs 9.4%; EPR, 3.7; 95% CI, 3.0-4.4). Decedents were more likely to have had chronic pain than the comparison group (94.2% vs 31.6%; EPR, 3.0; 95% CI, 2.7-3.3). CONCLUSIONS: Use of pain medication outside prescription bounds was a risk factor for death. However, decedents were more likely to have had chronic pain, and the majority of both groups had obtained pain medication by prescription. Other factors (e.g., smoking status) might also play important roles in prescription opioid-related death. Prescribers should screen chronic pain patients for risk factors.

Outbreak of Shiga-toxigenic Escherichia coli O157:H7 infections associated with rodeo attendance, Utah and Idaho, 2009.

OBJECTIVES: In summer 2009, the Utah Department of Health investigated an outbreak of Shiga-toxigenic Escherichia coli (STEC) O157:H7 (O157) illness associated with attendance at multiple rodeos. MATERIALS AND METHODS: Patients were interviewed regarding exposures during the week before illness onset. A ground beef traceback investigation was performed. Ground beef samples from patient homes and a grocery store were tested for STEC O157. Rodeo managers were interviewed regarding food vendors present and cattle used at the rodeos. Environmental samples were collected from rodeo grounds. Two-enzyme pulsed-field gel electrophoresis (PFGE) and multiple-locus variable-number tandem repeat analysis (MLVA) were performed on isolates. RESULTS: Fourteen patients with primary STEC O157 illness were reported in this outbreak. Isolates from all patients were indistinguishable by PFGE. Isolates from nine patients had identical MLVA patterns (main outbreak strain), and five had minor differences. Thirteen (93%) patients reported ground beef consumption during the week before illness onset. Results of the ground beef traceback investigation and ground beef sampling were negative. Of 12 primary patients asked specifically about rodeo attendance, all reported having attended a rodeo during the week before illness onset; four rodeos were mentioned. All four rodeos had used bulls from the same cattle supplier. An isolate of STEC O157 identified from a dirt sample collected from the bullpens of one of the attended rodeos was indistinguishable by PFGE and MLVA from the main outbreak strain. DISCUSSION: Recommendations were provided to rodeo management to keep livestock and manure separate from rodeo attendees. This is the first reported STEC O157 outbreak associated with attendance at multiple rodeos. Public health officials should be aware of the potential for rodeo-associated STEC illness.

Studying adverse events related to prescription opioids: the Utah experience.

BACKGROUND: Epidemiologists at the Utah Department of Health (UDOH) began to study prescription drug-related harm in 2004. We have analyzed several types of data including vital statistics, medical examiner records, emergency department diagnoses, and the state prescription registry to estimate the scope and correlates of prescription drug-related harm. OBJECTIVES: To describe data sets analyzed in Utah related to the problem of prescription drug-related harm with the goal of designing interventions to reduce the burden of adverse events and death. RESULTS: Prescription drug-related harm in Utah primarily involved opioids and can be examined with secondary analysis of administrative databases, although each database has limitations. CONCLUSIONS: More analyses, likely from cohort studies, are needed to identify risky prescribing patterns and individual-level risk factors for opioid-related harm. Combining data sets via linkage procedures can generate individual-level drug exposure and outcome histories, which may be useful to simulate a prospective cohort.

State-level strategies for reducing prescription drug overdose deaths: Utah's prescription safety program.

INTRODUCTION: The Utah Department of Health created a program to decrease deaths and other harm from prescription pain medication. Program goals included educating the public, providers, and patients on prescription safety and creating guidelines for providers on prescribing opioids. PROGRAM INTERVENTIONS: The department's Prescription Pain Medication Program was organized in collaboration with many state agencies as well as public and private organizations. The program developed a statewide media campaign, running messages using the slogan "Use Only As Directed" from May 2008 to May 2009. The program facilitated the publication and distribution of opioid prescribing guidelines. PROGRAM OUTCOMES: Collaboration among stakeholders to develop educational materials furthered use of the materials. The program distributed more than 2,800 copies of the prescribing guidelines and more than 120,000 copies of print materials, including bookmarks, patient information cards, and posters. STATEWIDE DATA: In 2008, unintentional overdose deaths from prescription opioids dropped 14.0% compared with the number of deaths in 2007. In 2009, the number of deaths remained stable from 2008. The campaign funding ended in May 2009. State agencies have continued collaborating and have pooled money to renew the media campaign in 2011. Evaluation of the impact of the prescribing guidelines is ongoing. CONCLUSIONS: The state-funded educational campaign may have contributed to a reduction in overdose deaths. Collaboration among state agencies and a sustained educational effort are important aspects of a successful prevention campaign.

Physician use of parasite tests in the United States from 1997 to 2006 and in a Utah Cryptosporidium outbreak in 2007.

Parasitic infection is uncommon in the United States, but surveys suggest that physicians test when the presence of parasites is unlikely and fail to order appropriate testing when suspicion is high. Numerous studies confirm that immunoassays are more sensitive for Giardia and Cryptosporidium detection, but our experience was that physicians preferentially used ovum and parasite examination (O&P). We conducted a retrospective study of fecal parasite testing at a referral laboratory nationally (1997 to 2006) and during a Cryptosporidium outbreak (Utah, 2007) to correlate physician use of O&P and enzyme immunoassays (EIAs) with the yield of parasites detected. Nationally, of 170,671 episodes, 76.0% (n = 129,732) included O&P, 27.9% (n = 47,666) included Giardia EIA, and 5.7% (n = 9,754) included Cryptosporidium EIA. Most pathogens were Giardia or Cryptosporidium. More episodes were positive when EIA was performed (n = 1,860/54,483 [3.4%]) than when O&P only was performed (n = 1,667/116,188 [1.4%]; P < 0.001), and EIA was more sensitive than O&P. However, more O&P results were positive among patients with both O&P and EIA performed (2.5%) than among those with O&P only performed (1.4%; P < 0.001), suggesting that patients tested by O&P only may have been at lower risk. During the first 10 weeks of the outbreak, physicians also preferentially used O&P over EIA, but no Cryptosporidium cases were detected by O&P. We conclude that clinicians frequently use O&P testing when test performance and epidemiology support the use of immunoassays or no testing. We recommend that stool O&P be limited to patients with negative immunoassay results and persistent symptoms or individuals at increased risk for non-Giardia, non-Cryptosporidium infection. An evidence-based algorithm for the evaluation of patients with suspected intestinal parasitic infection is proposed.

Strengthening Partnerships along the Informatics Innovation Stages and Spaces: Research and Practice Collaboration in Utah.

Collaborate, translate, and impact are key concepts describing the roles and purposes of the research Centers of Excellence (COE) in Public Health Informatics (PHI). Rocky Mountain COE integrated these concepts into a framework of PHI Innovation Space and Stage to guide their collaboration between the University of Utah, Intermountain Healthcare, and Utah Department of Health. Seven research projects are introduced that illustrate the framework and demonstrate how to effectively manage multiple innovations among multiple organizations over a five-year period. A COE is more than an aggregation of distinct research projects over a short time period. The people, partnership, shared vision, and mutual understanding and appreciation developed over a long period of time form the core and foundation for ongoing collaborative innovations and its successes.

Tularemia outbreak associated with outdoor exposure along the western side of Utah Lake, Utah, 2007.

OBJECTIVES: In 2007, a localized outbreak of tularemia occurred among visitors to a lodge on the western side of Utah Lake, Utah. We assessed risk factors for disease and attempted to identify undiagnosed clinically compatible illnesses. METHODS: We conducted a retrospective cohort study by recruiting all people who had visited the lodge on the western side of Utah Lake from June 3 to July 28, 2007. A self-administered questionnaire was distributed to a sub-cohort of people who were part of an organized group that had at least one tularemia patient. Questions assessed risk and protective factors and disease symptoms. RESULTS: During the outbreak period, 14 cases of tularemia were reported from five of Utah's 12 health districts. The weekly attack rate ranged from 0 to 2.1/100 lodge visitors from June 3 to July 28. Illness onset dates ranged from June 15 to July 8. The median delay between onset of symptoms and laboratory test for tularemia was 14 days (range: 7-34 days). Cohort study respondents who reported deer-fly bites while at the lodge (adjusted risk ratio [ARR] = 7.2, 95% confidence interval [CI] 2.4, 22.0) and who reported having worn a hat (ARR = 5.6, 95% CI 1.3, 24.6) were more likely to become ill. CONCLUSIONS: This was Utah's second documented deer-fly-associated human tularemia outbreak. People participating in outdoor activities in endemic areas should be aware of disease risks and take precautions. Educational campaigns can aid in earlier disease recognition, reporting, and, consequently, outbreak detection.

Feasibility of elementary school children's use of hand gel and facemasks during influenza season.

BACKGROUND: The feasibility of non-pharmacologic interventions to prevent influenza's spread in schools is not well known. OBJECTIVES: To determine the acceptability of, adherence with, and barriers to the use of hand gel and facemasks in elementary schools. INTERVENTION: We provided hand gel and facemasks to 20 teachers and their students over 4 weeks. Gel use was promoted for the first 2 weeks; mask use was promoted for the second 2 weeks. OUTCOMES: Acceptability, adherence, and barriers were measured by teachers' responses on weekly surveys. Mask use was also measured by observation. RESULTS: The weekly survey response rate ranged from 70% to 100%. Averaged over 2 weeks, 89% of teachers thought gel use was not disruptive (week 1--17/20, week 2--16/17), 95% would use gel next winter (week 1--19/20, week 2--16/17), and 97% would use gel in a pandemic (week 1--20/20, week 2--16/17). Averaged over 2 weeks, 39% thought mask use was not disruptive (week 1--6/17, week 2--6/14), 35% would use masks next winter (week 1--5/17, week 2--6/14), and 97% would use masks in a pandemic (week 1--16/17, week 2--14/14). About 70% estimated that their students used hand gel ≥ 4 x/day for both weeks (week 1--14/20, week 2--13/17). Students' mask use declined over time with 59% of teachers (10/17) estimating regular mask use during week 1 and 29% (4/14) during week 2. By observation, 30% of students wore masks in week 1, while 15% wore masks in week 2. Few barriers to gel use were identified; barriers to mask use were difficulty reading facial expressions and physical discomfort. CONCLUSIONS: Hand gel use is a feasible strategy in elementary schools. Acceptability and adherence with facemasks was low, but some students and teachers did use facemasks for 2 weeks, and most teachers would use masks in their classroom in a pandemic.

Utah clinical guidelines on prescribing opioids for treatment of pain.

Utah Clinical Guidelines on Prescribing Opioids for Treatment of Pain were produced and made available to medical providers in March 2009. These guidelines were developed by a multidisciplinary consensus panel after a review of existing evidence-based guidelines. Common recommendations were compiled and presented to the panel for review. The guidelines consist of a set of recommendations for both acute and chronic pain. A second panel reviewed existing tools for providers and determined the need for any new tools. The final guidelines include 20 tools for providers to use in their practice. The complete version of the guidelines and the accompanying tools are available at: www.useonlyasdirected.org or www.health.utah.gov/prescription.

Clinical findings and demographic factors associated with ICU admission in Utah due to novel 2009 influenza A(H1N1) infection.

BACKGROUND: Novel 2009 influenza A(H1N1) infection has significantly affected ICUs. We sought to characterize our region's clinical findings and demographic associations with ICU admission due to novel A(H1N1). METHODS: We conducted an observational study from May 19, 2009, to June 30, 2009, of descriptive clinical course, inpatient mortality, financial data, and demographic characteristics of an ICU cohort. A case-control study was used to compare the ICU cohort to Salt Lake County residents. RESULTS: The ICU cohort of 47 influenza patients had a median age of 34 years, Acute Physiology and Chronic Health Evaluation II score of 21, and BMI of 35 kg/m2. Mortality was 17% (8/47). All eight deaths occurred among the 64% of patients (n = 30) with ARDS, 26 (87%) of whom also developed multiorgan failure. Compared with the Salt Lake County population, patients with novel A(H1N1) were more likely to be obese (22% vs 74%; P < .001), medically uninsured (14% vs 45%; P < .001), and Hispanic (13% vs 23%; P < .01) or Pacific Islander (1% vs 26%; P < .001). Observed ICU admissions were 15-fold greater than expected for those with BMI > or = 40 kg/m2 (standardized morbidity ratio 15.8, 95% CI, 8.3-23.4) and 1.5-fold greater than expected among those with BMI of 30 to 39 kg/m(2) for age-adjusted and sex-adjusted rates for Salt Lake County. CONCLUSIONS: Severe ARDS with multiorgan dysfunction in the absence of bacterial infection was a common clinical presentation. In this cohort, young nonwhites without medical insurance were disproportionately likely to require ICU care. Obese patients were particularly susceptible to critical illness due to novel A(H1N1) infection.

Spinach-associated Escherichia coli O157:H7 outbreak, Utah and New Mexico, 2006.

In 2006, Utah and New Mexico health departments investigated a multistate cluster of Escherichia coli O157:H7. A case-control study of 22 case-patients found that consuming bagged spinach was significantly associated with illness (p<0.01). The outbreak strain was isolated from 3 bags of 1 brand of spinach. Nationally, 205 persons were ill with the outbreak strain.

Risk factors for pediatric invasive pneumococcal disease in the Intermountain West, 1996-2002.

PURPOSE: In response to concerns that the epidemiology of pediatric invasive pneumococcal disease (IPD) in the Intermountain West (i.e., Utah, Idaho, Wyoming, Montana, and parts of Arizona and Nevada) was poorly understood and might differ from elsewhere in the United States, a case-control study was undertaken to determine factors associated with IPD during 1996-2002. METHODS: A telephone questionnaire was administered to parents of children comprising 120 cases identified through hospital records and to parents of 156 age-matched controls located by random-digit dialing. The unit of analysis was each matched case-control set. RESULTS: Underlying chronic illness was reported for 32 (27%) of the cases. For previously healthy children, breastfeeding had a protective benefit (adjusted odds ratio: 0.2; 95% confidence interval [CI], 0.1-0.6), while a history of tympanostomy tube surgery was a risk factor (adjusted odds ratio: 12.6; 95% CI, 1.5-107.3). CONCLUSIONS: The presence of an underlying chronic illness was the strongest risk factor for IPD. Except for a history of tympanostomy tube surgery, the factors associated with IPD in this investigation were similar to those reported from other geographic regions. Tympanostomy surgery might serve as a surrogate indicator for predisposition to recurrent otitis media or decreased ability to clear pneumococcal infection, raising risk for invasive disease. Pediatric clinicians should continue to encourage breastfeeding, and continued emphasis on pneumococcal vaccination should help prevent IPD.

Informing the front line about common respiratory viral epidemics.

The nature of clinical medicine is to focus on individuals rather than the populations from which they originate. This orientation can be problematic in the context of acute healthcare delivery during routine winter outbreaks of viral respiratory disease where an individuals likelihood of viral infection depends on knowledge of local disease incidence. The level of interest in and perceived utility of community and regional infection data for front line clinicians providing acute care is unclear. Based on input from clinicians, we developed an automated analysis and reporting system that delivers pathogen-specific epidemic curves derived from a viral panel that tests for influenza, RSV, adenovirus, parainfluenza and human metapneumovirus. Surveillance summaries were actively e-mailed to clinicians practicing in emergency, urgent and primary care settings and posted on a web site for passive consumption. We demonstrated the feasibility and sustainability of a system that provides both timely and clinically useful surveillance information.

Validity of electronic medical record-based rules for the early detection of meningitis and encephalitis.

Diseases of the central nervous system (CNS) such as meningitis or encephalitis may represent events of public health interest due to emerging infections and/or NIH/CDC Category B priority pathogens. Apart from influencing treatment and management of the index case, some diagnoses such as meningococcal meningitis warrant an immediate public health response. Others such as West Nile Virus may require public education and vector control. Thus early detection of CNS syndromes is of benefit to patients, providers and public health. While computer-based surveillance methods have been used with success in the early detection of respiratory syndromes, there is little data on their use in CNS syndromes. This study analyzed the validity of a hospital emergency department computer-based surveillance system in the early detection of meningitis and encephalitis and determined the test characteristics of selected computer-based rules.

Vaccine effectiveness during a varicella outbreak among schoolchildren: Utah, 2002-2003.

OBJECTIVES: In the context of a chickenpox outbreak involving 2 Utah elementary schools, we conducted an investigation to assess vaccine effectiveness, describe illness severity, and examine risk factors for breakthrough varicella (ie, varicella in those who have been vaccinated). METHODS: All parents were asked to complete a questionnaire about their child's medical history. Parents of children with recent varicella were interviewed, and vaccination records were verified. Lesions were submitted for polymerase chain reaction testing. RESULTS: Questionnaires were returned for 558 (93%) of 597 students in school A and 924 (97%) of 952 students in school B. A total of 83 schoolchildren (57 unvaccinated and 26 vaccinated) had varicella during the October 2002 through February 2003 outbreak period. An additional 17 cases occurred among household contacts, including infants and adults. Polymerase chain reaction analysis recovered wild-type varicella. Vaccine effectiveness was 87%. With 1 notable exception, vaccinated children tended to have milder illness. Risk factors for breakthrough varicella included eczema, vaccination > or =5 years before the outbreak, and vaccination at < or =18 months of age. Restricting analysis to children vaccinated > or =5 years before the outbreak, those vaccinated at < or =18 months of age were more likely to develop breakthrough varicella (relative risk: 9.3; 95% confidence interval: 1.3-68.9). CONCLUSIONS: The vaccine, administered by >100 health care providers to 571 children during a 7-year time period, was effective. Risk factors for breakthrough varicella suggest some degree of biological interaction between age at vaccination and time since vaccination.