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PubMed1995

Evaluation of phenotypic and genotypic methods for epidemiological typing of Staphylococcus aureus isolates from bovine mastitis in Denmark.

The value of five different typing methods (antibiogram typing, biotyping, phage typing, plasmid profiling and restriction fragment length polymorphism of the gene encoding 16S and 23S ribosomal RNA (ribotyping)), in discriminating 105 Staphylococcus aureus strains from bovine milk samples obtained from 105 different Danish dairy herds was investigated. A total of 85 strains (81%) proved susceptible to all of the 11 antibiotics tested, and the remaining 20 strains could be divided into 5 different antibiogram patterns. The predominant resistance pattern, penicillin resistance, was observed in 15 (75%) of the 20 antibiotic resistant strains. Biotyping assigned the strains to 14 different types, with the most common type accounting for 25.7% of the strains. Ninety eight (93.3%) strains could be typed by phages, assigning them to 19 different phage types. The predominant phage type accounted for 31.4% of the strains. Eight different plasmid profiles was observed among 24 (23%) strains harbouring plasmids. Ribotyping yielded 30 different types, with the most common accounting for 29.5% of the strains. The single most discriminatory typing method was ribotyping (0.863) followed by biotyping (0.842) and phage typing (0.795). Plasmid profiling (0.395) and antibiogram typing (0.327) had low discriminatory indices. Correspondence among ribotypes and the presence or absence of plasmids were observed, as was some degree of correspondence between ribotype, phage type and biotype. In general the correspondence between phage type and ribotype were stronger than between biotype and ribotype and between biotype and phage type. All combinations of two or more methods led to an improved index of discrimination compared to the individual methods indicating, that some subdivision of types had taken place. The combination of phage, bio- or ribotyping or all three methods in combination are considered to be an efficient combination of typing methods for epidemiological investigation of S. aureus mastitis.

Animals↗
PubMed2005

In vitro antimicrobial susceptibility, genetic diversity and prevalence of UDP-glucose 4-epimerase (galE) gene in Campylobacter coli and Campylobacter jejuni from Turkey production facilities.

This study evaluated the genetic diversity of multi-drug resistant Campylobacter jejuni (n=44) and C. coli (n=30) isolated from 18 turkey houses. Antimicrobial resistances to ampicillin, ciprofloxacin and nalidixic acid were higher (P<0.05) in C. coli than in C. jejuni strains. PCR analysis indicated that 82% of total isolates tested, including 91% of C. jejuni and 70% of C. coli tested positive for a 496-bp UDP-glucose 4-epimerase (galE) gene. The diversity of isolates was mapped by antibiogram, SmaI-PFGE and flaA-RFLP typing methods using the discriminatory index (DI). RFLP was more suitable in discriminating C. coli (DI=0.895) than PFGE (DI=0.816) or antibiogram profile (DI=0.552), while either PFGE (DI=0.941) or RFLP (DI=0.942) could be used in discriminating C. jejuni strains. The combined PFGE and antibiogram dendrogram had the highest DI for both C. coli (0.910) and C. jejuni (0.968), suggesting that a combination of typing methods is more useful in examining the diverse Campylobacter population on turkey farms.

Animals↗
PubMed2006

[Obtention of bacterial antibiotic susceptibility following standard conditions directly from infected biological fluids and positive blood cultures].

OBJECTIVE: Determining the conditions, which would allow us to apply bacterial antibiotic susceptibility tests directly to infected biological fluids and positive blood cultures and in accordance with the standard conditions of these tests. METHODS: For infected fluids (N=23), a correlation was determined between the bacterial count observed by microscopic field on a cystopin centrifugation pellet and the dilution required to obtain bacterial inocula corresponding to those used in the standard antibiogram and E-test methods. For blood cultures detected positive with the BactALERT system (26 Enterobacteriaceae, 29 Staphylococcus and 11 Pneumococcus), the broth dilution required to obtain such inocula was determined for each bacterial type. RESULTS: For infected fluids, the dilution required for the antibiogram of enterobacterial and staphylococcal isolates was respectively of 10(-1) and 10(0) when there were 50 to 100 bacteria/field, 10(-2) and 10(-1) for 100 to 500, 10(-3) and 10(-2) for 500 to 1000, and 10(-4) and 10(-3) for>1000. A minimum of 50 to 100 bacteria/field was required to determine beta-lactam MICs towards a pneumococcal isolate present in cerebrospinal fluid. For blood cultures, a broth dilution of 10(-4) for Enterobacteriaceae and of 10(-2) for Staphylococcus and Pneumococcus allowed to reproduce the standard antibiogram. To reproduce the standard conditions of the E-test method for beta-lactam MICs towards a pneumococcal isolate, the broth dilution was 10(-1). CONCLUSION: Following the procedure described, antibiotic susceptibility can be available 24 h earlier.

Anti-Bacterial Agents↗
PubMed2005

Molecular characterization of Staphylococcus intermedius carriage by healthy dogs and comparison of antimicrobial susceptibility patterns to isolates from dogs with pyoderma.

We conducted an epidemiological study of Staphylococcus intermedius using arbitrarily primed PCR (AP-PCR) and antibiograms. One hundred and twenty-five S. intermedius isolates were recovered from the oral cavity and/or cranial hair coat of healthy dogs enrolled in a pet therapy program. Commensal S. intermedius was cultured from 32% of the oral cavity cultures and 13% of the cranial hair coat cultures. We characterized the colonization of the dogs as transient, intermittent, or persistent. For dogs characterized as persistently colonized, 73% of the isolates came from the oral cavity. These isolates were also genotyped by AP-PCR. A single major AP-PCR type was observed in 91% of the dogs (n=22); minor variations were frequently observed in these major types. Antibiograms of these commensal isolates were compared to antibiograms from 97 historical clinical isolates (1988-1992) obtained from cases of canine pyoderma. Resistance was most often observed to penicillin (64% and 55%) and tetracycline (38% and 38%) among the commensal and clinical isolates, respectively. The commensal isolates were significantly less resistant to erythromycin, clarithromycin, clindamycin, and trimethoprim/sulfamethoxazole. Our data suggests that differences in both genotype and antimicrobial susceptibility phenotypes exist among S. intermedius strains isolated from different anatomic sites from the same dog and supports the opportunistic nature of S. intermedius in canine infections.

Animals↗
PubMed1996

A comparison of methods to determine whether clinical isolates of Staphylococcus epidermidis from the same patient are related.

Staphylococcus epidermidis is a major cause of hospital-acquired infections but also part of the normal skin flora. A common clinical question is whether repeated isolation of S. epidermidis from one patient represents the same strain; because if different strains are isolated, they are often thought to be contaminants. In this study, different typing methods were compared to answer this question. Twenty isolates of S. epidermidis from five different patients were investigated. The isolates from each patient had identical or very similar antibiograms, and were recovered on different occasions. Typing was performed by antibiogram, biotype, slime production, plasmid profile, and pulsed-field gel electrophoresis (PFGE) banding pattern of SmaI digests of chromosomal DNA. In addition, the level of resistance to methicillin was determined by growth curves in broth containing methicillin for a series of different inocula for each isolate. The results showed that the isolates from each patient belonged to the same clone, but examples of instabilities in their antibiograms, plasmid profiles, as well as their PFGE banding patterns were seen. A change in the level of methicilli, resistance was observed in one strain; otherwise this characteristic was found to be strain-specific and stable in vivo. It was concluded that in combination with biotyping and antibiotic resistance testing the level of resistance to methicillin could be used as an aid to distinguish between two or more clinical isolates of S. epidermidis from the same patient.

Bacterial Typing Techniques↗
PubMed1981

Comparison of four methods of differential typing of isolates of Shigella sonnei.

An epidemiological study of Sonne dysentery in Dundee during the years 1971-6 was made by examining, in respect of 1420 isolates of Shigella sonnei, the discriminating power of colicine typing, antibiogram testing, biotyping and resistotyping and the stabilty of the markers they provided. Colicine typing identified nine colicine types, including four not previously described. However, because types 4 and 4 var., determined by col Ib, and type U, producing no colicines, accounted for 96% of the isolates, discrimination with colicine typing was poor. In antibiotic sensitivity test, 13 different antibiogram patterns were noted. Less than 1% of the isolates were sensitive to all of the eight antibiotics tested; most were multiply drug-resistant. Resistance to kanamycin, neomycin and paromomycin (KNP) was apparently due to a single resistance determinant, widely distributed in a majority (53%) of the isolates. When definitive times were chosen for reading each biotyping test, only maltose and rhamnose of the 13 "sugars' tested differentiated isolates into prompt- and late-fermenting types. Though the ability to ferment rhamnose was a stable property, it discriminated only 1.5% of the minority, late-fermenting type. Resistotyping with six chemicals discriminated eight epidemiologically valid resistotypes, including three new types. However, 93 of the isolates belonged to only three resistotypes. Analysis of the data for isolated from 286 epidemiologically distinct episodes showed that the variability of colicine and antibiogram characters, found among isolates within, respectively, 40 and 28% of the episodes, was generally associated with loss or gain of a plasmid ("col Ib-KNP') which determined production of colicine Ib and KNP resistance. These characters varied both in vivo and in vitro. Variability of resistotype characters, on the other hand, was observed in only 28 (9%) episodes, 14 of which possibly represented examples of mixed or sequential infections. For accurate epidemiological tracing of strains of Sh. sonnei in a community, resistotyping, the technique showing the greatest discrimination and least variability of the four tested, should be included as the principal typing method.

Anti-Bacterial Agents↗
PubMed1984

Three clusters of Bacillus pseudobacteremia related to a radiometric blood culture analyzer.

During a ten-month period from September 1981 to July 1982 three episodes of pseudobacteremia due to Bacillus species occurred at this 550-bed institution. The first involved eight isolates, the second 11, and the third seven isolates of the organism, all with the same antibiogram. The patients involved did not exhibit clinical signs of septicemia, and in only one case was more than one specimen per patient positive when multiple blood samples were obtained. Occasional blood cultures of Bacillus species identified in between clusters revealed a different antibiogram. Extensive epidemiologic investigation of patient locations, phlebotomists, and time of cultures yielded no common source. Components involved in the transport and processing of blood cultures, including the radiometric blood culture processor, were also sampled but without recovery of the organism. After the last episode, a layer of dust was noted inside the machine, and culture of this dust grew Bacillus spp. with the same antibiogram as those found in the blood cultures. The filter from an air conditioning unit in close proximity to the machine grew several species of Bacillus. It is presumed that Bacillus spores in the dust were introduced into the blood culture bottles following the heat sterilization of the gas sampling (inoculation/removal) needles. Modification of the cover of the machine was undertaken to prevent access of dust bearing microbes to the inside of the machine. In addition, maintenance now includes regular disinfection/cleaning of the "floor" of the machine, and more frequent changes of the air conditioner filter.

Autoanalysis↗
PubMed1990

Drug-resistant coagulase-negative skin staphylococci. Evaluation of four marker systems and epidemiology in an orthopaedic ward.

Drug-resistant coagulase-negative staphylococci (DRCNS) in orthopaedic patients and ward staff were studied. A significant increase in the DRCNS carriage rate was observed among the 16 patients studied after 14 days of hospitalization with levels approaching that of the staff. Patients receiving dicloxacillin prophylaxis (n = 9) were more likely to be colonized with methicillin-resistant CNS, while patients receiving no antibiotics (n = 7) became to a larger extent colonized with multiple DRCNS. The combined data from species determination, biochemical, plasmid, and antibiogram typing revealed a considerable diversity among DRCNS; 64 types were distinguished among 112 DRCNS isolates selected for study after exclusion of apparently duplicate isolates. Plasmid plus antibiogram typing yielded almost as many types (61); whereas species determination plus antibiogram distinguished only 33 types. Although a novel computerized 96-reaction biotyping method alone enabled differentiation of 17 biotypes, most DRCNS isolates belonged to one of three major biotypes limiting the usefulness of this method. Ten of the 64 (16%) DRCNS types identified comprised 50 of the 112 (45%) isolates. These were isolated from staff and from patients on day 14, suggesting a nosocomial origin.

Adult↗
PubMed1990

Use of plasmid analysis to determine the source of bacterial invasion of the urinary tract.

Gram negative colonisation and infection of the urinary tract is a well recognised complication of the neuropathic bladder caused by spinal cord injury (SCI). K. pneumoniae accounts for one third of all urinary tract infections in hospitalised SCI patients. Plasmid analysis has been shown to reliably fingerprint bacterial strains, particularly K. pneumoniae, so that growth from two separate locations in or on the body can be accurately analysed as to migration from a reservoir to a target location. Eighty seven hospitalised SCI patients on intermittent catheterisation for a total of 586 patient-weeks were studied. Twice weekly catheterised urine specimens and once weekly rectal swab cultures were taken from each patient. Thirty seven patients experienced at least one clinically significant (colony count greater than 10,000/mL) urinary tract colonisation caused by K. pneumoniae, representing 66 total colonisations. Further analysis of 31 of these 37 patients revealed: K. pneumoniae in all of their stool cultures (p less than 0.05) and the identical strain of K. pneumoniae in the urine as well as the stool in 72% of the 66 colonisations (p less than 0.05). Analysis of 14 patients without K. pneumoniae urinary colonisations showed absence of faecal K. pneumoniae in 3, and predominant growth in only 4. In 22 of the 37 patients, multiple K. pneumoniae urinary colonisations were noted, representing 27 pairs of colonisation. Fifteen of the pairs were found to be relapsing (caused by two identical bacterial strains), and 12 were recurrent (caused by two different bacterial strains). Thirteen of the 15 relapsing pairs also had identical urine and stool K. pneumonia strains (p less than 0.05). All colonisations were treated with appropriate antibiotics based on culture and sensitivity reports. Fourteen of the 15 relapsing colonisation pairs have identical antibiograms (p less than 0.05), while all 12 of the recurrent colonisation pairs had different antibiograms (p less than 0.05). The differences noted on sensitivity patterns (antibiograms) correlated with differences among strains of K. pneumoniae based upon plasmid analysis. Treatment of bacteriuria did not affect the nature of repeated colonisations regardless of the antibiotic chosen, the route of administration or the duration of treatment.

Adolescent↗
PubMed2000

Use of RAPD-ALF analysis for investigating the frequency of bacterial cross-transmission in an adult intensive care unit.

Bacterial cross-transmission was investigated during a 12-month period in an adult intensive care unit (ICU) by the generation of random amplified polymorphic DNA (RAPD) fingerprinting profiles, combined with automated laser fluorescence (ALF) analysis. The potential episodes of cross-transmission identified, were compared with those detected by the conventional first-line screen of antibiogram typing. Over the year, 215 primary gram-negative bacterial isolates were obtained from 160 patients. In total, 22 possible episodes of cross-transmission, involving 70 (44%) of the 160 patients, were identified by RAPD-ALF analysis, and 19 of these were substantiated with epidemiological evidence. Conversely, 31 possible episodes were identified on the basis of antibiogram data, but only three of these episodes, two involving Acinetobacter baumannii and one involving Serratia marcescens, correlated with those identified by RAPD-ALF analysis. It was concluded that analysis of antibiogram data alone is an unreliable method for assessing bacterial cross-transmission, unless the organism involved has a particularly stable or unusual resistance pattern. In contrast, the technique of RAPD-ALF analysis may provide a rapid and simple technique for obtaining an insight into the population dynamics of gram-negative bacteria in adult ICUs.

Acinetobacter↗
PubMed2001

Typing of Acinetobacter baumannii isolated from hospital-acquired respiratory infections in a tertiary care centre in southern India.

In an attempt to define the epidemiology of Acinetobacter baumannii infection, 27 isolates, obtained from hospital-acquired respiratory infections, were typed using random amplified polymorphic DNA (RAPD) profile and antimicrobial susceptibility patterns. Ten different patterns were obtained with ERIC2 primer: 14 isolates had a similar profile representing a single strain. Within RAPD types, isolates could be further classified based on their antibiogram; however, strains of different types had similar antibiograms. This study showed that many different genetic types of A. baumannii are prevalent in our hospital. While antibiograms alone are not sufficiently discriminatory, RAPD typing helps in identifying outbreaks and in assessing infection control procedures within a hospital.

Academic Medical Centers↗
PubMed1999

Investigation of suspected nosocomial clusters of Staphylococcus haemolyticus infections.

OBJECTIVE: To determine whether typing methods can discriminate among Staphylococcus haemolyticus isolates. DESIGN: Molecular epidemiological evaluation of S. haemolyticus isolates obtained from patients hospitalized on a hematology service and in a surgical intensive-care unit (SICU). SETTING: A large Midwestern teaching hospital. INTERVENTIONS: None. RESULTS: Over 22 days, S. haemolyticus was isolated from five patients on the hematology service. Isolates from four patients had the same unusual antibiogram and biotype. Ribotyping, restriction endonuclease digestion of plasmid DNA (REAP), and whole chromosomal DNA analysis by pulsed-field gel electrophoresis (PFGE) confirmed that these isolates were identical and different from the fifth patient's isolate and from 6 control isolates. In a second cluster, 11 S. haemolyticus isolates obtained from eight patients in the SICU had similar antibiograms and biotypes. By REAP and ribotype analysis, isolates from four patients were identical. However, PFGE indicated that only two of these patients shared a common strain. CONCLUSIONS: Antibiograms or biotyping may discriminate among isolates of S. haemolyticus if the results of these tests are unusual. Many clinical isolates can be differentiated by REAP analysis, ribotyping, or PFGE. However, some isolates are identical by all of these methods, suggesting that they may have been transmitted nosocomially.

Cross Infection↗
PubMed2001

Antibiotic resistance is a major risk factor for epidemic behavior of Acinetobacter baumannii.

OBJECTIVE: To study the presence of bacterial factors in clinical isolates of Acinetobacter species in order to identify markers of epidemic potential. DESIGN: Case-control study. METHODS: Forty-six isolates of Acinetobacter species, including 23 epidemic and 23 sporadic strains from different outbreaks in nine European countries, were compared for the presence of the following factors: hemagglutination, presence of capsules and fimbriae, binding to salivary mucins, resistance to drying, and antibiogram typing. Genotyping of all strains was performed by amplified fragment-length polymorphism (AFLP). RESULTS: All outbreak strains except two (91%) were identified as Acinetobacter baumannii. Binding to salivary mucins and resistance to antibiotics were significantly associated with epidemic behavior. Antibiogram typing showed clustering of predominantly A baumannii strains within one group, and these strains were significantly more resistant to antibiotics than sporadic strains. AFLP genotyping revealed a great heterogeneity among the different European Acinetobacter strains. Cluster analysis of AFLP fingerprints showed several small clusters of different A baumannii outbreak strains. AFLP genotyping could not identify a common epidemic marker within the strains studied. CONCLUSIONS: Antibiogram typing can be used in routine clinical laboratories as a screening method to recognize potentially epidemic A baumannii strains. Several other factors were found, both in different outbreaks as well as in sporadic Acinetobacter isolates. These characteristics were unable to predict epidemic behavior and therefore cannot be used as discriminative epidemic markers. AFLP genotyping demonstrated no common clonal origin of European epidemic A baumannii strains. This indicates that any clinical A baumannii isolate with resistance to multiple antibiotics can be a potential nosocomial outbreak strain.

Acinetobacter↗
PubMed2004

Surveillance in Taiwan using molecular epidemiology for extended-spectrum beta-lactamase-producing Klebsiella pneumoniae.

OBJECTIVE: To evaluate intrahospital and interhospital clonal dissemination of extended-spectrum beta-lactamase (ESBL)-producing strains of Klebsiella pneumoniae. SETTING: Eight tertiary-care university hospitals and 16 regional hospitals in Taiwan. METHODS: Two hundred eleven confirmed ESBL-producing isolates of K. pneumoniae were collected from January 1998 to June 2000. The isolates were characterized by various typing methods, including antibiogram (9 antimicrobial agents), computer-based ribotyping, pulsed-field gel electrophoresis (PFGE), and isoelectric focusing of beta-lactamase. RESULTS: Ribotyping identified 70 distinct ribogroups among 200 isolates evaluated. Forty-three of these ribogroups were unique. Eleven ribogroups, comprising 115 isolates, were detected in more than one hospital (interhospital dissemination), whereas 16 groups (42 isolates) were detected in more than one patient within a hospital (intrahospital dissemination). The combination of ribotyping and PFGE identified two large epidemic clones, which were called 691.5/PFGE-G and 595.7/PFGE-A. These epidemic clones were detected mainly in the hospitals located in the northern and central regions of Taiwan. However, variation of the profiles of antibiograms and isoelectric focusing was apparent within each clone. In addition, isolates with the same isoelectric focusing profile (isoelectric points 7.9, 8.2, and 8.4) and antibiogram (resistance to 9 compounds evaluated) were present among different molecular-typed clones. CONCLUSIONS: Our results showed that clonal dissemination (both interhospital and intrahospital dissemination) is occurring in several regions of Taiwan. Rapid computer-based ribotyping associated with PFGE demonstrated multiple epidemic clones of ESBL-producing K. pneumoniae in Taiwan. The combination of phenotypic and molecular methods has proved useful to characterize these epidemic clones.

Clone Cells↗
PubMed1994

Analysis of epidemic and endemic isolates of Xanthomonas maltophilia by contour-clamped homogeneous electric field gel electrophoresis.

BACKGROUND: Xanthomonas maltophilia is increasingly a cause of nosocomial infections. The mode of transmission of this organism is not well known. OBJECTIVE: To investigate clonality of X maltophilia isolates in epidemic and endemic settings. METHODS: An outbreak of X maltophilia was noted in the Intensive Care Nursery (ICN). Over the ensuing 9 months, hospital wide isolates of X maltophilia were analyzed using contour-clamped homogeneous electric field (CHEF) gel electrophoresis of chromosomal DNA. This method was compared with the antibiogram for detecting differences and similarities among strains. RESULTS: X maltophilia was recovered from 76 sites in 72 patients; 65 isolates from 61 patients and the hands of one nurse were available for analysis. CHEF demonstrated differences between most epidemiologically unrelated strains and similarity between most epidemiologically related strains. Several strains, initially presumed to be related because of temporal and spatial proximity of the patients involved, were determined by CHEF analysis to be independent infections. One pair of isolates whose XbaI CHEF patterns differed by a single band were differentiated clearly by SspI. There was enough variation in the minimum inhibitory concentrations of selected antibiotics to allow typing of some strains. The antibiogram, however, did not group all of the ICN outbreak isolates with others found to be genetically identical by CHEF, and it grouped 39 of 56 isolates with others not genetically the same. CONCLUSIONS: Although it is a convenient and economical tool, the antibiogram has limitations. Analysis by CHEF should help to elucidate the epidemiological spread of X maltophilia in the hospital.

Adult↗
PubMed1995

Focused microbiological surveillance and gram-negative beta-lactamase--mediated resistance in an intensive care unit.

OBJECTIVE: To evaluate the use of focused surveillance in following resistance patterns within an intensive care unit (ICU). DESIGN: Antibiograms of 167 gram-negative isolates from ICU patients were compared to the hospitalwide antibiograms. ICU isolates were examined for the newer forms of beta-lactamase resistance. An outbreak of multiresistant Pseudomonas aeruginosa during the survey illustrated the usefulness of focused surveillance in early intervention and containment. SETTING: A 700-bed adult tertiary care hospital with a 16-bed medical and surgical ICU. RESULTS: Hospitalwide and ICU antibiograms of the Enterobacteriaceae were similar. However, resistance of P aeruginosa in the ICU was underestimated by hospitalwide rates. Susceptibility of ICU isolates to ceftazidime, ciprofloxacin, and piperacillin was 54%, 54%, and 42%, compared with 81%, 77%, and 85%, respectively, in the hospital at large. Thirty-five percent of isolates exhibited one of the newer forms of beta-lactamase-mediated resistance, with 17% of isolates exhibiting Class I cephalosporinase production. CONCLUSION: Targeted survey of high antibiotic-use hospital units should be used to study bacterial epidemiology, rather than relying on general hospital data to evaluate patterns of antimicrobial resistance. Monitoring of potential problem areas leads to prompt identification of changes in resistance and allows early intervention.

Adult↗
PubMed1980

Plasmid profiles in epidemiologic studies of infections by Staphylococcus epidermidis.

Plasmid profiles of cultures of Staphylococcus epidermidis obtained by agarose gel electrophoresis were used, in conjunction with phage typing, biotyping, and antibiograms, in epidemiologic studies of infections in neonates and patients with cancer. In some cases, patients had cultures that were lysed by a single phage, belonged to the same biotype, and had identical antibiograms, but had distinctly different plasmid profiles. In other instances, almost identical plasmid profiles were observed in cultures lysed by a single phage, belonging to the same biotype, and with markedly different antibiograms. The plasmid profile technique was valuable in detecting distinct strains of S. epidermidis, and its use could be helpful in epidemiologic studies of infections by other organisms.

Bacteriological Techniques↗
PubMed1978

Raw hamburger: an interstate common source of human salmonellosis.

An interstate common-source outbreak of salmonellosis was first detected in the United States in September and October, 1975, when a tenfold increase in Salmonella newport isolates was noted through routine salmonella surveillance by the Colorado Department of Health. Eighteen primary cases with a distinctive antibiotic resistance pattern (tetracycline, streptomycin, and sulfonamides) were evaluated in a case-control study, and illness was found to be associated with eating raw hamburger (p less than .001) from any store of one grocery chain (p less than .001). A Dallas, Texas, processing plant that supplied the Colorado markets also supplied other states, and these other states were alerted. Maryland discovered nine S. newport isolates with the same antibiogram and, as in the Colorado outbreak, illness was associated with eating raw or very rare ground beef from the same grocery chain (p less than .03). A third outbreak of S. newport with the same antibiogram occurred on a Florida military base. S. newport with the same antibiogram and a phage lysis pattern identical to those of the human epidemic isolates was cultured from frozen hamburger recovered in Colorado and Florida. The associated hamburger originated at the same Dallas, Texas, processing plant. A source of the epidemic strain was not identified, but the organism probably originated before delivery to the plant.

Adolescent↗