An outbreak of 2009 pandemic influenza A (H1N1) virus infection in an elementary school in Pennsylvania.

In May 2009, one of the earliest outbreaks of 2009 pandemic influenza A virus (pH1N1) infection resulted in the closure of a semi-rural Pennsylvania elementary school. Two sequential telephone surveys were administered to 1345 students (85% of the students enrolled in the school) and household members in 313 households to collect data on influenza-like illness (ILI). A total of 167 persons (12.4%) among those in the surveyed households, including 93 (24.0%) of the School A students, reported ILI. Students were 3.1 times more likely than were other household members to develop ILI (95% confidence interval [CI], 2.3-4.1). Fourth-grade students were more likely to be affected than were students in other grades (relative risk, 2.2; 95% CI, 1.2-3.9). pH1N1 was confirmed in 26 (72.2%) of the individuals tested by real-time reverse-transcriptase polymerase chain reaction. The outbreak did not resume upon the reopening of the school after the 7-day closure. This investigation found that pH1N1 outbreaks at schools can have substantial attack rates; however, grades and classrooms are affected variably. Additional study is warranted to determine the effectiveness of school closure during outbreaks.

Two outbreaks of severe respiratory disease in nursing homes associated with rhinovirus.

OBJECTIVES: To characterize illness and identify the etiology for two nursing home outbreaks of respiratory illness. DESIGN: Multisite outbreak investigations; cohort. SETTING: Two nursing homes in Pennsylvania. PARTICIPANTS: Facility A residents (n = 170), Facility B residents (n = 124), and employees (n = 91). MEASUREMENTS: Medical records for Facility A and B residents were reviewed, and employees from Facility B self-administered a questionnaire to identify risk factors for illness. Serological, oropharyngeal, and nasopharyngeal specimens were collected for both outbreaks, and testing for respiratory pathogens was performed. RESULTS: In Facility A, 40 (24%) of 170 residents were identified with respiratory illness; 13 (33%) case-patients had radiographically confirmed pneumonia, 15 (38%) were taken to a hospital, and two (5%) died. Of 10 specimens collected from symptomatic Facility A case-patients, four (40%) tested positive using reverse transcription polymerase chain reaction for rhinovirus. In Facility B, 77 (62%) of 124 residents had respiratory illness, and 40 (52%) had radiographically confirmed pneumonia; 12 (16%) case-patients were hospitalized, and five (6%) died. Of 19 respiratory specimens collected from symptomatic Facility B case-patients, six (32%) were positive for rhinovirus; one was from an employee. Five (50%) of 10 rhinovirus-positive cases in both outbreaks had clinical and radiographic evidence of pneumonia. CONCLUSION: These investigations suggest that rhinoviruses may be an underrecognized cause of respiratory outbreaks in nursing homes, capable of causing pneumonia and perhaps death.

A limited measles outbreak in a highly vaccinated US boarding school.

OBJECTIVES: We investigated a measles outbreak that began in March 2003 in a Pennsylvania boarding school with >600 students to identify all cases, including the source; implement outbreak control measures; and evaluate vaccine effectiveness. METHODS: Measles was suspected in any person at the school with a generalized rash and fever during March 21 to May 28, 2003 and investigated with serologic testing. We reviewed vaccination history from school records and conducted a survey to determine country of measles vaccination. Vaccine effectiveness was calculated using the cohort method. RESULTS: We identified 9 laboratory-confirmed cases at the school: 8 students and 1 staff member. Among them, 2 had never received any doses of measles-containing vaccine (MCV), 1 received 1 dose of MCV, and 6 received 2 doses of MCV. Three of the 6 who received 2 doses of MCV received both doses outside the United States. The source case had been infected in Lebanon. Two laboratory-confirmed spread cases were identified in New York City. Measles virus of genotype D4 was isolated in cases from the school and New York City. Of the 663 students in the school, 8 (1.2%) had never received any doses of MCV, 26 (3.9%) had received 1 dose, and 629 (94.9%) had received 2 doses before the outbreak. Vaccine effectiveness among students who had received 2 doses of MCV was 98.6%. However, students who received both doses outside the United States had a higher attack rate (3 of 75) than those who received both doses in the United States (3 of 509; rate ratio: 6.8; 95% confidence interval: 1.4-33.0). CONCLUSIONS: This is the largest measles outbreak to occur in a school in the United States since 1998, but it was limited to only 9 cases in a boarding school with >600 students. The limited extent of this outbreak highlights the high level of population immunity achieved in the United States through widespread implementation of a 2-dose measles-mumps-rubella vaccination strategy in school-aged children. States and schools should continue to enforce strictly the 2-dose measles-mumps-rubella vaccination requirement and, in an outbreak setting, consider revaccinating students who received measles vaccine outside of the United States. Continued vigilance by health care providers is needed to recognize measles cases.

It's not the heat, it's the humidity: wet weather increases legionellosis risk in the greater Philadelphia metropolitan area.

BACKGROUND: Legionella species are abundant in the environment and are increasingly recognized as a cause of severe pneumonia. Increases in cases of community-acquired legionellosis in the greater Philadelphia metropolitan area (GPMA) led to concern that changing environmental factors could influence occurrence of disease. METHODS: We evaluated the association between weather patterns and occurrence of legionellosis in the GPMA, using both traditional Poisson regression analysis and a case-crossover study approach. The latter approach controls for seasonal factors that could confound the relationship between weather and occurrence of disease and permits the identification of acute weather patterns associated with disease. RESULTS: A total of 240 cases of legionellosis were reported between 1995 and 2003. Cases occurred with striking summertime seasonality. Occurrence of cases was associated with monthly average temperature (incidence rate ratio [IRR] per degree Celsius, 1.07 [95% confidence interval [CI], 1.05-1.09]) and relative humidity (IRR per 1% increase in relative humidity, 1.09 [95% CI, 1.06-1.12]) by Poisson regression analysis. However, case-crossover analysis identified an acute association with precipitation (odds ratio [OR], 2.48 [95% CI, 1.30-3.12]) and increased humidity (OR per 1% increase in relative humidity, 1.08 [95% CI, 1.05-1.11]) 6-10 days before occurrence of cases. A significant dose-response relationship for occurrence of cases was seen with both precipitation and increased humidity. CONCLUSIONS: Although, in the GPMA, legionellosis occurred predominantly during summertime, the acute occurrence of disease is best predicted by wet, humid weather. This finding is consistent with the current understanding of the ecological profile of this pathogen and supports the contention that sporadic legionellosis occurs through contamination of water sources.

Necrotizing enterocolitis associated with clostridium perfringens type A in previously healthy north american adults.

BACKGROUND: Necrotizing enteritis associated with Clostridium perfringens type C ("pigbel") is a well-known syndrome in severely protein-deprived populations in the Pacific. It is exceedingly rare in the developed world. C perfringens type A is a common cause of acute gastroenteritis and, in a handful of infections, has been reported in association with a syndrome resembling necrotizing enteritis. STUDY DESIGN: This study includes a case series and literature review. Charts and autopsy reports from four patients with adult necrotizing enterocolitis (ANEC) were reviewed. C perfringens isolates were subtyped by mouse bioassay and pulsed-field gel electrophoresis. Fixed tissue specimens were tested with an anticlostridial antibody using an immunohistochemical assay. RESULTS: Between 2000 and 2003, ANEC developed in four previously healthy men; three died. The small bowel was affected in three patients and the colon in two patients. Portal or mesenteric vein thrombosis occurred in three patients. C perfringens type A was isolated from three patients and immunohistochemical assay demonstrated clostridial antigens limited to affected areas of the intestine of all four. The nonculture positive patient had a strong epidemiologic link to one of the others, and a compatible clinical course. C perfringens of the same pulsed-field gel electrophoresis-defined molecular subtyped was isolated from stool samples of one patient, his wife, and food from a restaurant they patronized. CONCLUSIONS: ANEC associated with C perfringens type A infection occurred in four North American adults. Culture for C perfringens type A should be performed in cases of ANEC. Alternative tests such as immunohistochemical assay were diagnostically useful. Additional research might uncover virulence factors, host factors, and the burden of disease in the population.

Younger age at vaccination may increase risk of varicella vaccine failure.

To determine vaccine effectiveness (VE), a varicella outbreak in a highly vaccinated day-care center (DCC) population in Pennsylvania was investigated. In Pennsylvania, proof of immunity is required for children >or=12 months old for DCC enrollment. Questionnaires were administered to parents of children who had attended the DCC continuously during the study period (1 November 1999-9 April 2000) to determine history of varicella disease or vaccination and for information about any recent rash illnesses. VE was calculated for children >or=12 months old without a history of varicella. There were 41 cases of varicella among 131 attendees, with 14 cases (34%) among vaccinated children. VE was 79% against all varicella and 95% against moderate or severe varicella. Vaccination at <14 months was associated with an increased risk of breakthrough disease (relative risk, 3.0; 95% confidence interval, 0.9-9.9). Despite varicella vaccination coverage of 80%, a sizeable outbreak occurred. Early age at vaccination may increase the risk of vaccine failure.