The changing epidemiology of salmonella: trends in serotypes isolated from humans in the United States, 1987-1997.

Salmonellosis is a major cause of illness in the United States. To highlight recent trends, data for 1987-1997 from the National Salmonella Surveillance System were analyzed. A total of 441,863 Salmonella isolates were reported, with the highest age-specific rate among infants (159/100,000 infants at 2 months). Annual isolation rates decreased from 19 to 13/100,000 persons; however, trends varied by serotype. The isolation rate of Salmonella serotype Enteritidis increased until 1996, whereas declines were noted in Salmonella serotypes Hadar and Heidelberg. Overall, serotypes that increased in frequency were significantly more likely than those that decreased to be associated with reptiles (P=.008). Salmonella infections continue to be an important cause of illness, especially among infants. Recent declines in food-associated serotypes may reflect changes in the meat, poultry, and egg industries that preceded or anticipated the 1996 implementation of pathogen-reduction programs. Additional educational efforts are needed to control the emergence of reptile-associated salmonellosis.

Supplement 2000 (no. 44) to the Kauffmann-White scheme.

This supplement reports the characterization of 12 new Salmonella serovars recognized in 2000 by the WHO Collaborating Centre for Reference and Research on Salmonella: nine were assigned to S. enterica subsp. enterica, two to subspecies salamae, and one to subspecies diarizonae.

Classification, identification, and clinical significance of Proteus, Providencia, and Morganella.

This review presents the current taxonomy of the genera Proteus, Providencia, and Morganella, along with the current methods for the identification of each species within the three genera, incorporating both conventional biochemical and commercial methods. While all of these organisms are ubiquitous in the environment, individual case reports and nosocomial outbreak reports that demonstrate their ability to cause major infectious disease problems are presented. Lastly, anticipated antimicrobial susceptibility patterns are reviewed. Many of these organisms are easily controlled, but the advent of newer and more powerful antimicrobial agents has led to some problems of which laboratorians need to be aware.

Classification of Proteus vulgaris biogroup 3 with recognition of Proteus hauseri sp. nov., nom. rev. and unnamed Proteus genomospecies 4, 5 and 6.

Strains traditionally identified as Proteus vulgaris formed three biogroups. Biogroup 1, characterized by negative reactions for indole production, salicin fermentation and aesculin hydrolysis, is now known as Proteus penneri. Biogroup 2, characterized by positive reactions for indole, salicin and aesculin, was shown by DNA hybridization (hydroxyapatite method) to be a genetic species separate from biogroup 1 and from biogroup 3 which is positive for indole production and negative for salicin and aesculin. In this study, 52 strains were examined, of which 36 strains were Proteus vulgaris biogroup 3, which included the current type strain of the species P. vulgaris (ATCC 29905T), and compared to seven strains of Proteus vulgaris biogroup 2 and nine type strains of other species in the genera Proteus, Providencia and Morganella. By DNA hybridization, these 36 strains were separated into four distinct groups, designated as Proteus genomospecies 3, 4, 5 and 6. DNAs within each separate Proteus genomospecies were 74-99% related to each other in 60 degrees C hybridization reactions with < or = 4.5% divergence between related sequences. Proteus genomospecies 3 contained the former P. vulgaris type strain and one other strain and was negative in reactions for salicin fermentation, aesculin hydrolysis and deoxyribonuclease, unlike the reactions associated with strains considered as typical P. vulgaris which are positive in reactions for salicin, aesculin and DNase. Genomospecies 3 can be distinguished from Proteus genomospecies 4, 5 and 6 because it is negative for Jordan's tartrate. Proteus genomospecies 4, containing five strains, was differentiated from Proteus penneri, genomospecies 3 and 6 and most, but not all, strains of genomospecies 5, by its ability to ferment L-rhamnose. Proteus genomospecies 5 and 6, containing 18 and 11 strains, respectively, could not be separated from each other by traditional biochemical tests, by carbon source utilization tests or SDS-PAGE of whole-cell proteins. In an earlier publication, a request was made to the Judicial Commission that the former type strain of P. vulgaris (ATCC 13315) be replaced by P. vulgaris biogroup 2 strain ATCC 29905T, a strain considered more biochemically typical of P. vulgaris strains. This would have the effect of assigning the name P. vulgaris to P. vulgaris biogroup 2. Since this request has been acceded to, the name Proteus hauseri is herein proposed for Proteus vulgaris genomospecies 3. Its type strain is ATCC 700826T. Proteus genomospecies 4, 5 and 6 will remain unnamed until better phenotypic differentiation can be accomplished. All Proteus genomospecies were similar in their antimicrobial susceptibility patterns. Nineteen strains were isolated from urine, four from faeces, two from wounds, nine from other human sources and two from animals.

Supplement 1998 (no. 42) to the Kauffmann-White scheme.

This supplement reports the characterization of 14 new Salmonella serovars recognized in 1998 by the WHO Collaborating Centre for Reference and Research on Salmonella: 11 were assigned to S. enterica subsp. enterica, one to subspecies salamae, one to subspecies diarizonae, and one to subsp. indica. In addition, the antigenic factor H:z88 is described.

Supplement 1999 (no. 43) to the Kauffmann-White scheme.

This supplement reports the characterization of 26 new Salmonella serovars recognized in 1999 by the WHO Collaborating Centre for Reference and Research on Salmonella: 15 were assigned to S. enterica subsp. enterica, seven to subspecies salamae, two to subspecies diarizonae, and one to subsp. houtenae; and one to S. bongori. In addition, the antigenic factor H:z89 is described.

Supplement 1997 (no. 41) to the Kauffmann-White scheme.

This supplement reports the characterization of 15 new Salmonella serovars recognized in 1997 by the WHO Collaborating Centre for Reference and Research on Salmonella: 8 were assigned to S. enterica subsp. enterica, 4 to subspecies salamae, 2 to subspecies diarizonae, and 1 to subsp. houtenae. In addition, the antigenic factors H:z85 and H:z87 are described and one modification to the Kauffmann-White scheme is reported.

Supplement 1996 (no. 40) to the Kauffmann-White scheme.

This supplement reports the characterization of 13 new Salmonella serovars recognized in 1996 by the WHO Collaborating Centre for Reference and Research on Salmonella: 8 were assigned to S. enterica subsp. enterica, 3 to subspecies salamae and 2 to subspecies diarizonae.

Recurrent outbreaks of Salmonella Enteritidis infections in a Texas restaurant: phage type 4 arrives in the United States.

In recent years infection caused by Salmonella serotype Enteritidis (SE) phage type 4 has spread through Europe but has been uncommon in the USA. The first recognized outbreak of this strain in the USA occurred in a Chinese restaurant in EI Paso, Texas, in April 1993; no source was identified. In September 1993, a second outbreak caused by SE phage type 4 was associated with the same restaurant. To determine the cause of the second outbreak, we compared food exposures of the 19 patients with that of two control groups. Egg rolls were the only item significantly associated with illness in both analyses (first control group: odds ratio [OR] 8.2, 95% confidence interval [CI] 2.3-31.6; second control group: OR 13.1, 95% CI 2.1-97.0). Retrospective analysis of the April outbreak also implicated egg rolls (OR 32.4, 95% CI 9.1-126.6). Egg roll batter was made from pooled shell eggs and was left at room temperature throughout the day. These two outbreaks of SE phage type 4 likely could have been prevented by using pasteurized eggs and safe food preparation practices.

Supplement 1994 (no. 38) to the Kauffmann-White scheme.

This supplement reports the characterization of 24 new Salmonella serovars recognized in 1994 by the WHO Collaborating Centre for Reference and Research on Salmonella: 11 were assigned to S. enterica subsp. enterica, 6 to subspecies salamae, 6 to subspecies diarizonae and 1 to subspecies houtenae. In addition, the antigenic factor H:z83 is described.

Replacement of NCTC 4175, the current type strain of Proteus vulgaris, with ATCC 29905. Request for an opinion.

The current type strain of Proteus vulgaris, NCTC 4175 (= ATCC 13315), differs substantially from typical strains of this species both biochemically and chemotaxonomically. DNA relatedness studies revealed that strains previously classified as P. vulgaris belong to six genomospecies. One of these genomospecies contains strains that are negative in indole, salicin, and esculin reactions (biogroup 1) and has been named Proteus penneri. A second genomospecies, which is most frequently isolated from human urine, contains typical P. vulgaris strains that are positive in indole, salicin, and esculin reactions (biogroup 2). The members of the remaining four genomospecies are indole positive and negative in salicin and esculin reactions (biogroup 3). Of 36 biogroup 3 strains studied, only strain NCTC 4175T (T = type strain) and one other strain, CDC 1732-80, belong to genomospecies 3. To retain NCTC 4175 as the type strain of P. vulgaris would restrict this species to these two strains, whose origins are unknown. This would mean that hundreds of strains for which the description of P. vulgaris was written and which have been representatives of this species for the past 50 years would have to be renamed as members of a new species. To prevent this confusion, we request that biogroup 2 reference strain ATCC 29905 (= CDC PR1) replace NCTC 4175 as the type strain of P. vulgaris.

Differentiation of Salmonella enteritidis phage type 8 strains: evaluation of three additional phage typing systems, plasmid profiles, antibiotic susceptibility patterns, and biotyping.

Three additional phage typing systems for Salmonella enteritidis, plasmid analysis, biochemical tests, and antimicrobial susceptibility tests, were used in an attempt to subdivide 30 phage type 8 (phage typing system used by the WHO International Center for Enteric Phage Typing, London, England) isolates. These isolates represented 18 different egg-related outbreaks (21 strains) and 9 reference strains or strains that were not egg-associated. Only 7 of the 30 strains (28%) were subdivided by one or more of the methods used; this included 3 of the 21 strains from egg-related outbreaks. Twenty-seven strains contained a 55-kb plasmid that is associated with S. enteritidis. Of 65 additional phages tested, 2 from the phage typing system obtained from the Pasteur Institute, Paris, France, were useful in differentiating the three strains that lacked the 55-kb plasmid. Although the results obtained for the 21 strains from egg-related outbreaks showed that the strains had minor phenotypic differences, the overall results suggested that the strains may represent a single clone. Studies are planned to test additional phages and other typing methods to see whether strains of phage type 8 can be further differentiated.

Salmonella enteritidis outbreak in a restaurant chain: the continuing challenges of prevention.

In 1990, a Salmonella enteritidis (SE) outbreak occurred in a restaurant chain in Pennsylvania. To determine its cause(s), we conducted a case-control study and a cohort study at one restaurant, and a survey of restaurants. Egg dishes were associated with illness (P = 0.03). Guests from one hotel eating at the restaurant had a diarrhoeal attack rate of 14%, 4.7-fold higher than among those not eating there (P = 0.04). There were no differences in egg handling between affected and unaffected restaurants. Eggs supplied to affected restaurants were medium grade AA eggs from a single farm, and were reportedly refrigerated during distribution. Human and hen SE isolates were phage type 8 and had similar plasmid profiles and antibiograms. We estimate the prevalence of infected eggs during the outbreak to be as high as 1 in 12. Typical restaurant egg-handling practices and refrigeration during distribution appear to be insufficient by themselves to prevent similar outbreaks.

Recognition of Morganella subspecies, with proposal of Morganella morganii subsp. morganii subsp. nov. and Morganella morganii subsp. sibonii subsp. nov.

The genus name Morganella was established within the family Enterobacteriaceae in 1978. Morganella morganii is the only species described thus far within this genus, and the name M. morganii has been accepted by usage in the scientific community for strains previously known as Proteus morganii. M. morganii isolates differ in their abilities to ferment trehalose and exhibit variable lysine and ornithine decarboxylase patterns, emphasizing the phenotypic heterogeneity within this species. Previous genetic studies failed to reveal separate entities within the genus Morganella. We observed some trehalose-fermenting strains with different lysine and ornithine decarboxylase patterns. Two strains were lysine and ornithine positive, 3 were lysine positive and ornithine negative, and 29 were lysine negative and ornithine positive. These strains and 25 non-trehalose-fermenting strains with different lysine and ornithine decarboxylase patterns were investigated. DNA-DNA hybridization studies and phenotypic characterizations revealed that M. morganii can be separated into three DNA relatedness groups and seven biogroups. Strains from DNA relatedness group 1 were trehalose negative, and strains from DNA relatedness groups 2 and 3 were trehalose positive. One biogroup from DNA relatedness group 2 was phenotypically indistinguishable from DNA relatedness group 3. On the basis of these studies, we propose that M. morganii be subdivided into M. morganii subsp. morganii (type strain ATCC 25830) containing biogroups A, B, C, and D (DNA relatedness group 1) and M. morganii subsp. sibonii (type strain 8103-85; = ATCC 49948) containing biogroups E, F, and G (DNA relatedness groups 2 and 3).

Comparison of plasmid profiles, phage types, and antimicrobial resistance patterns of Salmonella enteritidis isolates in the United States.

To evaluate the laboratory techniques for subtyping isolates of Salmonella enteritidis, we compared the plasmid profiles (PP), phage types (PT), and antimicrobial susceptibility patterns (AS) of two nationally representative samples of sporadic human S. enteritidis isolates from 1979 (n = 28) and 1984 (n = 37), 43 isolates from 20 outbreaks of S. enteritidis infections between 1983 and 1987, and 46 animal isolates selected from the U.S. Department of Agriculture Veterinary Services Laboratory in 1986 and 1987. Sporadic and outbreak isolates from humans showed similar rates of resistance to at least one of a panel of antimicrobial drugs (23 and 14%, respectively), PT (91 and 98%, respectively), and PP (97 and 100%, respectively). Sixteen different PP were identified in sporadic, outbreak, and animal isolates; two PP accounted for 76% of sporadic and outbreak isolates. Sporadic human isolates were of PT 8 (42%), of PT 13a (37%), nontypeable (9%), of PT 14b (8%), of PT 9a (3%), and of PT 13 (2%). Outbreak human isolates had similar distributions of PT. PT 8 was associated with poultry: 58% (7 of 12) of the poultry isolates but only 24% (8 of 34) of the isolates from other animals were of PT 8 (P less than 0.04). Although antimicrobial susceptibility patterns do not appear as useful as an epidemiologic marker, PP and PT effectively subtyped S. enteritidis.

Phage typing of Salmonella enteritidis in the United States.

The number of reported isolates of Salmonella enteritidis has increased dramatically in the last 10 years. For many years phage typing has been a useful epidemiologic tool for studying outbreaks of S. typhi and S. typhimurium. In 1987, Ward et al. (L. R. Ward, J. De Sa, and B. Rowe, Epidemiol. Infect. 99:291-294, 1987) described a phage typing scheme for S. enteritidis. This system differentiated 27 phage types by use of 10 typing phages. With these phages, we typed 573 strains of S. enteritidis from humans (42 outbreaks), animals, food, and the environment. Ninety-six percent of the strains were typeable. The most common phage types were 8 (48.2%), 13a (20.1%), 13 (7.8%), and 14b (7.8%). Most of the strains were specifically collected from egg-related outbreaks in the northeastern United States in 1988 and 1989, probably accounting for the distribution of the four most common types in this sample. This system was particularly useful for differentiating a group of animal strains that had a number of diverse phage types. For 49 animal strains typed, 16 different patterns were obtained. Phage type 8 represented 32% of these strains, but no other phage type represented more than 8% of these strains. One-half of the 16 animal strains that were phage type 8 were from poultry. This phage typing system will be useful for comparing phage types found in the United States with those types encountered worldwide and for determining whether virulent strains of phage type 4 are entering the United States. Additional phage typing systems as well as molecular techniques are being studied to determine whether they can differentiate strains of phage types 8 and 13a.

Comparison of a latex agglutination assay and an enzyme-linked immunosorbent assay for detecting cholera toxin.

To determine the pandemic potential of Vibrio cholerae, one must demonstrate both the presence of O1 antigen and the production of enterotoxin (CT). Tissue culture or enzyme-linked immunosorbent assays (ELISAs) for CT have been limited to research and reference laboratories. A kit for detecting CT by reversed passive latex agglutination is now commercially available and was used to test 168 strains of V. cholerae O1 and non-O1. When compared with the routine ELISA, the latex test was 98% accurate (86 of 88) for serogroup O1 strains and 100% accurate (80 of 80) for non-O1 strains. For both O1 and non-O1 study strains, the sensitivity of the latex agglutination test was 0.97 and the specificity was 1.00 when results were compared with ELISA results. The latex test is commercially available and has the advantages of being less complicated and less time-consuming than the ELISA.

Ribosomal RNA gene restriction patterns provide increased sensitivity for typing Salmonella typhi strains.

To date, epidemiologic associations among strains of Salmonella typhi are based exclusively on phage typing, which may be of limited value if a common phage type is involved. Analysis of ribosomal RNA gene restriction patterns allows separation of most independently isolated strains of identical phage types. The sensitivity of the method is dependent on the restriction enzymes used to digest chromosomal DNA. It was highest for PstI, which separated 16 of 20 strains that belonged to 8 phage types including 3 untypable strains. Three strains differed in their phage types but had identical ribosomal RNA gene restriction patterns. Also, two pairs of strains indistinguishable by phage typing exhibited identical patterns; however, two of these strains were expected to be identical because they were isolated from two patients who were likely exposed to the same source. Ribosomal RNA gene restriction patterns appear to be stable. Thus, the method may complement phage typing and aid in further differentiation of strains.