Quasisteady aero-acoustic response of orifices.

The low frequency response of orifices (slit, circular diaphragm, and perforated plate) in the presence of mean flow is well predicted by a quasisteady theory. A refinement is brought to the theory by considering a Mach number dependent vena contracta coefficient. The measurements of the vena contracta coefficient of a slit agree well with the simple analytical expression existing in the case of the Borda tube orifice. The measured scattering matrix coefficients do not depend strongly on the geometry of the element. If the frequency is increased the moduli remain relatively unaffected while the arguments exhibit a complex behavior which depends on the geometry. From these considerations an anechoic termination efficient at high mass flow is designed.

Evaluation of pulsed-field gel electrophoresis in epidemiological investigations of meningococcal disease outbreaks caused by Neisseria meningitidis serogroup C.

Since 1990, the frequency of Neisseria meningitidis serogroup C (NMSC) outbreaks in the United States has increased. Based on multilocus enzyme electrophoresis (MEE), the current molecular subtyping standard, most of the NMSC outbreaks have been caused by isolates of several closely related electrophoretic types (ETs) within the ET-37 complex. We chose 66 isolates from four well-described NMSC outbreaks that occurred in the United States from 1993 to 1995 to evaluate the potential of pulsed-field gel electrophoresis (PFGE) to identify outbreak-related isolates specific for each of the four outbreaks and to differentiate between them and 50 sporadic isolates collected during the outbreak investigations or through active laboratory-based surveillance from 1989 to 1996. We tested all isolates collected during the outbreak investigations by four other molecular subtyping methods: MEE, ribotyping (ClaI), random amplified polymorphic DNA assay (two primers), and serotyping and serosubtyping. Among the 116 isolates, we observed 11 clusters of 39 NheI PFGE patterns. Excellent correlation between the PFGE and the epidemiological data was observed, with an overall sensitivity of 85% and specificity of 71% at the 95% pattern relatedness breakpoint using either 1.5 or 1.0% tolerance. For all four analyzed outbreaks, PFGE would have given public health officials additional support in declaring an outbreak and making appropriate public health decisions.

Disco fever: epidemic meningococcal disease in northeastern Argentina associated with disco patronage.

Neisseria meningitidis is a leading cause of adult meningitis worldwide. From 5 to 14 August 1996, 8 cases of meningococcal disease occurred in Corrientes city (population 306,000) in northeastern Argentina. Those infected ranged in age from 15 to 45 years (median, 18.5). To determine risk factors for infection, a case-control study was done. Infecting isolates were serogrouped and underwent phenotyping by multilocus enzyme electrophoresis (MLEE) and pulsed-field gel electrophoresis (PFGE). Those infected were significantly more likely than those not infected to have had exposure to passive or active cigarette smoke or to have attended a particular disco. Isolates available from 6 case-patients were all serogroup C; all had identical MLEE and PFGE patterns. These data suggest that dance clubs or discos may be a focus of transmission of N. meningitidis among young people.

Evaluation of silica gel packages for transport of Neisseria meningitidis.

Eight Neisseria meningitidis reference strains, representing six different serogroups, were plated on 57 blood agar plates each. The growth was harvested and stored in silica gel packages at different temperatures for up to 90 days. When held at 4 degrees C, all strains were recovered after 90 days of storage. Strains held at room temperature or alternately at 4 degrees C and room temperature survived for at least 10 and 17 days, respectively.

Molecular epidemiology of sporadic (endemic) serogroup C meningococcal disease.

Understanding the basis of sporadic (endemic) meningococcal disease may be critical to prevention of meningococcal epidemic outbreaks and to understanding fluctuations in incidence. Active, prospective, population-based surveillance and molecular epidemiologic techniques were used to study sporadic serogroup C meningococcal disease in a population of 2.34 million persons (Atlanta area). During 1988-1994, in which no outbreaks or case clusters were reported, 71 patients developed sporadic serogroup C meningococcal disease (annual incidence, 0.51/100,000). Eighty-three percent of patients were >2 years old. By multilocus enzyme electrophoresis, pulsed-field gel electrophoresis, and serotyping, 84% (52/62) of the isolates available for study were identical or closely related members of the electrophoretic type 37 (ET 37) complex responsible for multiple serogroup C outbreaks in the United States in the 1990s. Sporadic disease caused by 9 clonal strains occurred over periods up to 4 years and accounted for 45% (28/62) of cases. Sporadic serogroup C meningococcal disease was most often due to a limited number of related strains that appear to slowly circulate in the population.

Molecular subtyping of Neisseria meningitidis serogroup B: comparison of five methods.

In order to compare methods for subtyping Neisseria meningitidis serogroup B isolates, 96 isolates obtained from various locations in the United States and northwestern Europe were subtyped by five methods: monoclonal antibody (MAb)-based serotyping and serosubtyping, DNA macrorestriction analysis by pulsed-field gel electrophoresis (PFGE), multilocus enzyme electrophoresis (MEE), ribotyping, and PCR-restriction fragment length polymorphism of the internally transcribed spacer region of the rRNA operon (ITS PCR-RFLP). All N. meningitidis serogroup B isolates were typeable by PFGE, MEE, ribotyping, and ITS PCR-RFLP. Only 44.8% of the isolates were completely typeable (both serotype and serosubtype determination) by MAb-based serotyping and serosubtyping. 60.4% of the isolates could be serotyped but not serosubtyped, and 90.6% of the isolates could be either serotyped or serosubtyped. Simpson's discrimination indices of diversity for the methods were as follows: PFGE, 99.7%; MEE, 99.4%; ribotyping, 98.8%; MAb serotyping, 75.8%; MAb serotyping and/or serosubtyping 97.5%; and ITS PCR-RFLP, 84.2%. The high degree of diversity observed by PFGE, MEE, and ribotyping can be explained by the fact that isolates were collected from different geographic locations at various times. PFGE, MEE, and ribotyping showed greater discriminatory abilities than MAb-based serotyping and serosubtyping or ITS PCR-RFLP.

A rapid dot immunoassay for detecting the Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius with a "flow through" device.

Brazilian purpuric fever (BPF) is a highly fatal pediatric disease that may follow an episode of purulent conjunctivitis caused by a virulent clone of Haemophilus influenzae biogroup aegyptius (Hae). Oral rifampin prophylaxis, by eliminating carriage of the BPF clone in children with conjunctivitis, may prevent onset of the systemic disease. A test to detect the BPF clone directly from eye swabs could identify those in need of prophylaxis. This is a preliminary report of a rapid dot immunoassay performed on a "flow-through" cartridge that was developed for use under field conditions. The test is based upon recognition of a unique epitope of the 25-kDa pilin protein on the surface of BPF clone cells by a monoclonal antibody. With 36 laboratory-maintained cultures of Hae (15 clone isolates and 21 others), sensitivity of the assay was 67% and specificity was 95%. When fimbrial-enriched (25-kDa+) phenotypes of five false-negative clone strains were prepared for use as test antigens, sensitivity rose to 100%. Evaluation of the immunoassay under field conditions is necessary to prove its efficacy.

Carriage of Haemophilus influenzae type b in children after widespread vaccination with conjugate Haemophilus influenzae type b vaccines.

Rates of invasive Haemophilus influenzae type b (Hib) disease in children decreased very rapidly after licensure of Hib conjugate vaccines. A role for a vaccine-related reduction in nasopharyngeal carriage of Hib has been suggested. We studied oropharyngeal carriage of Hib and vaccination rates in a population of 2- to 5-year-old children in metropolitan Atlanta. Among 584 children 75% were vaccinated with an Hib conjugate vaccine, 17% had not been vaccinated and 8% had no vaccination records available. Forty-one percent of the children were colonized with H. influenzae. One child was colonized with Hib. Hib carriage (0.17%; upper 95% confidence interval boundary, 0.97%) was substantially lower than the estimates of Hib carriage from prior studies of children who had not received Hib conjugate vaccines. Our data are consistent with a decline in Hib carriage induced by widespread use of conjugate Hib vaccines, which may have contributed to the decline of Hib disease in United States children.

Comparison of cold enrichment and U.S. Department of Agriculture methods for isolating Listeria monocytogenes from naturally contaminated foods. The Listeria Study Group.

We compared the cold enrichment (CE) and U.S. Department of Agriculture (USDA) methods for isolating Listeria monocytogenes by examining 402 food samples. The food samples were collected from refrigerators of listeriosis patients as part of a multistate active surveillance project to determine the role of foods in sporadic listeriosis in the United States. L. monocytogenes was isolated from 51 food samples (13%). The USDA method was significantly better (P less than 0.001) than the CE method. The isolation efficiencies of the USDA and CE methods were 96 and 59%, respectively. Quantitation of L. monocytogenes in the food samples revealed that many food samples containing less than 0.3 CFU/g were negative as determined by the CE method but positive as determined by the USDA method.

A cluster of meningococcal disease on a school bus following epidemic influenza.

An outbreak of meningococcal disease among children on a school bus offered the opportunity to study a proposed association between this infection and preceding influenza infection. Five students who rode the bus became ill with invasive group C meningococcus. Transmission was limited to the bus; there was no evidence for school transmission. All five students reported influenza-like symptoms within several weeks before the development of meningococcal disease. School absenteeism, principally due to upper respiratory tract illness, was higher during the 3 weeks before the outbreak of meningococcal disease than during any period in the preceding 3 1/2 years, suggesting an unusually severe outbreak of respiratory illness. A case-control study comparing students with and without influenza symptoms revealed that the outbreak of respiratory disease was due to B/Ann Arbor/1/86 influenza (geometric mean titers, 86 for 80 patients and 33 for 47 controls [P = .0007]). These data add to the evidence suggesting that influenza respiratory infection predisposes to meningococcal disease.

Group A meningococcal carriage in travelers returning from Saudi Arabia.

In August 1987, an outbreak of group A meningococcal meningitis occurred during the annual pilgrimage to Mecca, Saudi Arabia, resulting in an attack rate among American pilgrims of 640 per 100,000. To determine risk factors for carriage, throat cultures were taken from passengers arriving on four consecutive flights from Saudi Arabia to the United States. Pilgrims were more likely to be group A meningococcal carriers than were nonpilgrims (relative risk, 11.1; 95% confidence interval, 3.7 to 33.1). Smoking, crowding, and meningococcal vaccination were not significantly associated with group A carriage. Pilgrims complaining of recent fever or sore throat, however, were more likely to be group A carriers, consistent with previous reports linking carriage and disease to preceding viral infections. Serogrouping of invasive meningococcal isolates can be used to monitor for indigenous transmission of this unusual strain in the United States, and we recommend routine vaccination of pilgrims to prevent future outbreaks of meningococcal disease.

Commercial latex agglutination tests for detection of Haemophilus influenzae type b and Streptococcus pneumoniae antigens in patients with bacteremic pneumonia.

The validity of commercial latex agglutination kits for detection of Haemophilus influenzae type b and Streptococcus pneumoniae antigens in serum and urine specimens was studied. We tested serum and urine specimens from 44 patients with bacteremic pneumonia (23 S. pneumoniae, 13 H. influenzae type b, 11 other) with commercial latex agglutination kits (Directigen, Bactigen) for S. pneumoniae and H. influenzae type b antigens. All specimen samples were randomized and read blindly by two readers. Interreader reproducibility was 100%. The sensitivity and specificity of both kits for H. influenzae type b antigens in serum and urine were greater than 90%. None of the 24 urine samples from S. pneumoniae bacteremic patients were positive by either kit, although 6 ng of type 3 polysaccharide could be detected in spiked urine. Sensitivity for S. pneumoniae antigens in serum was 27% for Directigen and 38% for Bactigen. Specificity for S. pneumoniae antigens in serum was 95% for Directigen and 74% for Bactigen. The results suggest that the kits are useful in diagnosing H. influenzae type b pneumonia. However, the commercially available S. pneumoniae reagents tested appear to have limited utility for diagnosing S. pneumoniae pneumonia because both kits lack sensitivity and Bactigen lacks specificity, as well.

Isolation of Listeria monocytogenes from raw milk.

During a recent outbreak of listeriosis, we examined 121 raw milk samples and 14 milk socks (filters). Listeria monocytogenes was recovered from 15 (12%) of 121 milk specimens and 2 (14%) of 14 milk socks. The optimal processing method consisted of cold enriching diluted milk for 1 month with culture to selective broth, followed by plating.

Age-specific differences in duration of clinical protection after vaccination with meningococcal polysaccharide A vaccine.

Sequential case-control studies were used to monitor changes in the clinical protection induced by group A meningococcal polysaccharide vaccine over a 3-year period. Overall, vaccine efficacy declined from 87% 1 year after vaccination to 70% and 54% at 2 and 3 years, respectively. When stratified by age at time of vaccination the data showed that, although vaccine efficacy remained high in children greater than or equal to 4 years of age (vaccine efficacy 85%, 74%, and 67% at 1, 2, and 3 years after vaccination, respectively), it declined dramatically in those less than 4 years of age at time of vaccination (vaccine efficacy 100%, 52%, and 8%, respectively, at 1, 2, and 3 years after vaccination). Thus, a single dose of group A meningococcal vaccine does not yield lasting clinical protection in children less than 4 years of age.

Trans-isolate medium: a new medium for primary culturing and transport of Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae.

A diphasic medium, Trans-Isolate medium, was developed for the transport of primary cultures of cerebrospinal fluids from patients with bacterial meningitis. It consists of a charcoal-starch agar slant and soybean-casein digest-gelatin broth buffered at pH 7.2 with 0.1 M 3-(N-morpholino)propanesulfonic acid buffer. In the laboratory, this medium supported the growth and survival of stock cultures of Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae for at least 3 months. Under field conditions in Africa, cerebrospinal fluids from patients suspected of having bacterial meningitis were inoculated directly onto plates of chocolate agar medium and into bottles of Trans-Isolate medium. An etiological agent was isolated from 52 spinal fluids by direct plating. After shipment to Atlanta, Ga., 2 to 4 weeks later, the same etiological agents were recovered from 38 bottles of Trans-Isolate medium.

Prevention of Hemophilus influenzae type b disease.

To determine the efficacy of rifampin prophylaxis in eradication of oropharyngeal carriage of Hemophilus influenzae type b and prevention of secondary H influenzae type b disease, we conducted a multicenter placebo-controlled trial among selected persons with invasive H influenzae type b disease. Households and day-care classrooms were randomized so that their members received either rifampin (initially at a dose of 10 mg/kg/dose for two to four days [rifampin-10], but subsequently at 20 mg/kg/dose for four days [rifampin-20]) or placebo. Pretherapy H influenzae type b colonization rates were similar in the treatment groups. Therapy with either rifampin regimen significantly reduced carriage (rifampin-20, 97%; rifampin-10, 63%; placebo, 28%). New acquisition of carriage was also significantly reduced by either rifampin regimen (rifampin-20 or rifampin-10, 2% v placebo, 6%). No rifampin-resistant H influenzae type b isolates emerged after treatment. Four of 765 placebo-treated contacts experienced secondary disease in contrast to zero of 1,112 rifampin-treated contacts. Because chemoprophylaxis of close contacts with rifampin seems to reduce significantly the risk of secondary H influenzae type b disease, we recommend the administration of prophylaxis in households or day-care classrooms where children younger than 4 years have been exposed to the disease.

In-vitro studies of interactions between tampons and Staphylococcus aureus.

In-vitro studies were done to investigate the role of tampons and Staphylococcus aureus in toxic shock syndrome. Tampons did not enhance the growth of S. aureus in nutrient broth or human blood. Intrinsic contamination of tampons with S. aureus was not found among the 504 tampons cultured (95% confidence limits of fraction contaminated; 0 to 0.007). Toxin-producing S. aureus persisted significantly longer on artificially contaminated Rely tampons (Procter & Gamble) than on the other brands tested. The proportion of clinical isolates of S. aureus capable of producing toxin increased from two of 36 in 1960 to eight of 20 in 1979 (p = 0.002, Fisher's exact test). This general increase in the proportion of toxin-producing strains may partially explain the increase in cases of toxic shock syndrome in recent years.