Use of Pulsed-Field Gel Electrophoresis for Investigation of a Cluster of Invasive Group A Streptococcal Illness—Spokane, Washington, 1999 FREE

MMWR. 1999;48:681-683

On January 25, 1999, health officials in Spokane County, Washington (1999 population: 415,000), were notified of a fatal case of necrotizing fasciitis (NF) caused by community-acquired invasive group A streptococcus (GAS) infection. Although invasive GAS infection is not a reportable disease in Washington, Spokane health officials requested reports of additional invasive GAS cases from local hospital infection-control professionals and the medical examiner to identify other cases. This report describes a cluster of fatal illnesses caused by GAS in five residents of Spokane County and illustrates how investigators used pulsed-field gel electrophoresis (PFGE) to determine whether the cluster was unrelated sporadic cases or attributable to a common source.

For this investigation, a case of invasive GAS infection was defined as any illness with onset after January 1, 1999, in a Spokane County resident with isolation of GAS from a normally sterile body site such as blood or deep muscle tissue. Medical records of each patient were reviewed, and at a University of Washington laboratory, GAS isolates from all patients were compared using PFGE with three separate enzymes (SmaI, ApaI, and SacII); GAS isolates also were T- and emm-typed at CDC.

Including the index case, five cases were identified, with illness onsets from January 25 through March 25. All cases were community acquired and fatal within 5 days of onset. All occurred in women aged 24-59 years. Four patients were morbidly obese (weights were 350, 374, and approximately 350 lbs; weight was not recorded for one). Four lived in the city of Spokane (1999 population: 189,000), and one lived in a nearby town. NF was diagnosed in four patients, and sepsis was diagnosed in one. GAS was isolated from both blood and wound tissue in three patients, from blood in one patient, and from a wound in one patient. Three had pre-existing skin breakdown at the NF site: one had had an open surgical abdominal wound for several months, one had chronic venous stasis of the legs with cellulitis and ulceration, and one had severe recurrent genital herpes.

GAS isolates from the five patients yielded four distinct PFGE patterns. The patterns of isolates from two patients were identical, while each pattern of the isolates from the other three patients was unique. Isolates from the two patients with identical PFGE patterns also had identical T- and emm-types (emm-type 1); isolates from the other three patients were unique (emm-types 3, 11, and 12). No epidemiologic relation between the two patients with identical isolates could be established. Prophylactic antibiotic treatment of close contacts was not pursued, and no secondary cases were identified.

P Stepak, MD, Spokane Health Dept, Spokane; MC Roberts, PhD, Univ of Washington School of Public Health, Seattle; M Goldoft, MD, J Kobayashi, MD, Washington State Health Dept. Respiratory Diseases Br, Div of Bacterial and Mycotic Diseases and Active Bacterial Core Surveillance/Emerging Infections Program Network, National Center for Infectious Diseases; and an EIS Officer, CDC.

The cases of GAS (i.e., Streptococcus pyogenes) infection described in this report were clustered in time and geographic area, suggesting they were epidemiologically related. Most cases of invasive GAS infection occur sporadically, although common-source outbreaks do occur, usually in long-term-care facilities or hospitals, especially among elderly, postsurgical, or postpartum patients.^1,2 Investigators from Spokane and the state health department used PFGE in their investigation to determine that these cases were not caused by a common source.

GAS is a common cause of pharyngeal, skin, and other soft tissue infections. Transmission of GAS is generally person to person through contaminated secretions. Rarely, infection results in invasive disease, with clinical manifestations that include NF, pneumonia, meningitis, puerperal sepsis, and streptococcal toxic shock syndrome (STSS). The case-fatality rate of invasive disease is approximately 15%, although this figure increases to >50% if STSS results.³ In 1998 in the United States, an estimated 10,000 cases and 1300 deaths resulted from invasive GAS infection, of which 4.6% were associated with NF.⁴

Risk factors for invasive GAS disease include diabetes, alcoholism, human immunodeficiency virus infection, malignancy, lack of skin integrity, recent surgery, abortion, or childbirth, and antecedent varicella in children.^5,6 Four of the women with invasive GAS infection described in this report were obese. Obesity has not been associated previously with invasive GAS infection and merits further study.

GAS strains can be serotyped (identification of M and T antigens) with specific antisera and by genetic sequencing of the 5‘ M-protein gene (emm) variable region.⁷ In the United States, the strains most likely to cause invasive infection are emm types 1, 3, and 12.^5,8 However, because these laboratory methods are not widely available and common-source community outbreaks are rare, GAS isolates from community-acquired cases are not routinely subtyped to determine relatedness. PFGE is widely available and discriminates GAS isolates effectively.⁹

This report provides evidence that PFGE can be useful for assisting epidemiologic investigations of illnesses caused by GAS. In this investigation, PFGE results were concordant with traditional typing methods, performed locally, and available within 4 days of submission of the isolates. The investigators used PFGE to determine that the five cases, despite their similarities, did not represent a common-source outbreak but were a clustering of sporadic cases. PFGE testing provided evidence that a search for a common-source for these infections, which would have required substantial public-health resources, was not warranted.

References: 9 available

MMWR. 1999;48:686-692

3 tables omitted

Tobacco use is the single leading preventable cause of death in the United States.¹ Preventing initiation of tobacco use is a public health priority. Approximately 80% of persons who use tobacco begin before age 18 years,¹ and the prevalence of cigarette smoking among high school students nationwide increased during the 1990s.² This report presents findings of a study that examined trends in cigarette smoking among high school students in 11 states that collected Youth Risk Behavior Survey (YRBS) data during the 1990s. In six of the 11 states, the prevalence of current smoking and frequent smoking increased among high school students.

The Youth Risk Behavior Surveillance System measures the prevalence of health-risk behaviors among adolescents through biennial representative school-based surveys conducted separately at the national, state, and local levels. In 1997, 39 states conducted YRBS. This report presents YRBS results from 11 state surveys conducted by state education and health agencies where representative data were obtained (i.e., a scientifically selected sample, an overall response rate of ≥60%, and appropriate survey documentation) in 1997 and in at least two additional years since 1991. The 1991, 1993, 1995, and 1997 state surveys used a two-stage cluster sample design to produce representative samples of 9th- to 12th-grade students in each participating state. Data were available from 1991 to 1997 in Alabama, South Carolina, South Dakota, and Utah and from 1993 to 1997 in Hawaii, Massachusetts, Mississippi, Montana, Nevada, Vermont, and West Virginia. Across all sites and years, sample sizes ranged from 1192 to 8636, school response rates ranged from 70% to 100%, student response rates ranged from 61% to 91%, and overall response rates ranged from 60% to 87%.

For each of the cross-sectional surveys, students completed an anonymous self-administered questionnaire that included questions about cigarette smoking. The wording of these questions was identical in each survey. Lifetime cigarette smoking was defined as having ever smoked cigarettes, even one or two puffs. Current cigarette smoking was defined as smoking on ≥1 of the 30 days preceding the survey, and frequent cigarette smoking was defined as smoking on ≥20 of the 30 days preceding the survey. Students were asked at what age they first smoked a whole cigarette. Beginning in 1993, students were asked whether they smoked cigarettes on school property on ≥1 of the 30 days preceding the survey.

Data were weighted to provide estimates generalizable to all public school students in grades 9-12 in each state. The relative percentage change in behavior from the earliest survey conducted (baseline) to 1997 was calculated as the 1997 prevalence minus the baseline prevalence divided by the baseline prevalence. SUDAAN was used for all data analysis. Secular trends were analyzed using logistic regression analyses that controlled for sex, grade, and race/ethnicity (except in Vermont, where students were not asked about race/ethnicity) and that simultaneously assessed linear and higher order (i.e., quadratic) time effects.³ Quadratic trends suggest a significant but nonlinear trend in the data over time. When the trend includes significant linear and quadratic components, the data demonstrate some nonlinear variation (e.g., leveling off or change in direction) in addition to a linear effect. In 1993, Alabama did not ask students about lifetime, current, or frequent smoking or the age at which students smoked their first cigarette; therefore, only linear trend analyses were performed for Alabama for those variables.

In South Carolina, South Dakota, and Vermont, lifetime smoking among high school students significantly increased linearly from baseline to 1997. The percentage increase in these states was 2%, 8%, and 5%, respectively. Massachusetts and Nevada showed significant quadratic trends, with the highest prevalence occurring in 1995.

The prevalence of current smoking significantly increased linearly in Alabama, Massachusetts, Mississippi, Montana, South Carolina, and South Dakota with percentage increases of 29%, 14%, 13%, 24%, 51%, and 42%, respectively. Massachusetts also showed a significant quadratic trend, with leveling between 1995 and 1997. South Carolina showed a significant quadratic trend, with leveling between 1991 and 1993 followed by increases in 1995 and 1997.

In Alabama, Massachusetts, Montana, South Carolina, South Dakota, and Vermont frequent smoking significantly increased linearly from baseline to 1997 with percentage increases of 26%, 19%, 52%, 39%, 49%, and 21%, respectively. Vermont also showed a significant quadratic trend, with leveling between 1995 and 1997.

The proportion of students who reported smoking a whole cigarette before age 13 years significantly decreased linearly from baseline to 1997 in Nevada and Utah. The percentage decrease was 17% in Nevada and 32% in Utah. Utah also showed a significant quadratic trend, with leveling between 1993 and 1995 before a decline in 1997.

In Alabama, Mississippi, South Carolina, and South Dakota, smoking on school property among high school students significantly increased linearly from 1993 to 1997. Percentage increases were 24%, 45%, 36%, and 32%, respectively.

Div of Adolescent and School Health and Office on Smoking and Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

For all five behaviors, trends among high school students in most of the 11 states were consistent with trends from the national YRBS.* From baseline to 1997, the prevalence of students reporting lifetime smoking remained stable in six states and across the nation,⁴ although in three states, lifetime smoking increased. The prevalence of current and frequent smoking increased in six states and remained stable in five states; in 1995, current smoking peaked in Massachusetts and frequent smoking leveled in Vermont. Across the nation, from 1991 to 1997, current smoking² and frequent smoking increased 32%⁴; from 1993 to 1997, current smoking increased 19%, and frequent smoking increased 21%.⁴ The percentage of students who reported smoking before age 13 years remained stable in nine states and across the nation⁴ and decreased in two states. Smoking on school property remained stable in six states and across the nation⁴ and increased in four states.

Additional research is needed to understand the variations between state and national trends. Differences in sociodemographic factors, efforts to prevent tobacco use, tobacco use policies, and enforcement of access laws may account for these variations. The tobacco industry's promotional strategies, such as reducing cigarette wholesale prices in Massachusetts following the January 1993 excise tax increase,⁵ also may have influenced state-specific trends.

The findings in this report are subject to at least three limitations. First, these data apply only to adolescents who attend public high school. In 1996, in the states for which data were available, high school dropout rates ranged from 2.9% to 9.6%.⁶ Second, the extent of underreporting or overreporting in YRBS cannot be determined, although the survey questions demonstrate good test-retest reliability.⁷ Finally, although the data for each state are representative of the students in that state, the states that were examined in this study may not be representative of all states.

To reduce tobacco use among youth, CDC recommends that states establish and sustain comprehensive tobacco-control programs.⁸ Although many states are allocating resources to tobacco control, no state is implementing all recommended program components. Comprehensive tobacco-control programs should reduce the appeal of tobacco products, implement youth-oriented mass media campaigns, increase tobacco excise taxes, and reduce youth access to tobacco products.¹ CDC's "Guidelines for School Health Programs to Prevent Tobacco Use and Addiction" recommends school-based tobacco-use prevention programs in grades K-12, with intensive instruction in grades 6-8.⁹ In support of this recommendation, CDC identifies evidence-based curricula to prevent tobacco use and addiction through its Research-to-Classroom program. These programs are most effective when linked to communitywide programs involving families, peers, and community organizations.⁹ The guidelines also recommend tobacco-free school-sponsored functions and tobacco-free school buildings, property, and vehicles. Consistent with these recommendations, the Pro-Children Act of 1994 requires smoke-free environments in schools receiving federal funds.¹⁰ However, most schools lack comprehensive prohibitions identified in the guidelines,¹⁰ and smoking on school property is increasing in some states.

The Youth Risk Behavior Surveillance System provides an important mechanism to track state progress in reducing tobacco use and other important health risk behaviors among youth. CDC provides support to every state to collect and use YRBS data. States also can conduct the Youth Tobacco Survey to obtain additional information about tobacco use and related factors.¹¹ If these efforts are expanded and maintained, all states could obtain data essential for planning and monitoring tobacco-use prevention programs for youth.

*The national YRBS is representative of high school students nationwide but does not provide state-specific estimates.