Insertion sequence IS200 fingerprinting of Salmonella typhi: an assessment of epidemiological applicability.

When Pst I-generated digests of genomic DNA from each of the type strains of 49 of the Vi phage types of Salmonella typhi were probed with a PCR-amplified IS200 gene probe, all strains were found to possess at least 11 IS200 elements carried on fragments in the range 24.2-1.2 kb. Fourteen fingerprints were identified but two patterns designated IS200Sty1 and IS200Sty2 predominated. In one strain, a plasmid-mediated IS200 element was identified. When IS200 fingerprinting was applied to epidemiologically-unrelated strains of S. typhi isolated in Ecuador, 3 patterns were identified in 10 strains belonging to 9 different phage types. It is concluded that Vi phage typing remains the method of choice for the primary differentiation of S. typhi but that IS200 fingerprinting may be of limited use in laboratories which do not have access to phage typing.     

Restaurant-associated outbreak of Salmonella typhi in Nauru: an epidemiological and cost analysis.

Typhoid fever is endemic in the South Pacific. We investigated an outbreak in Nauru. Through interviews and medical records, we identified 50 persons with onset between 1 October 1998 and 10 May 1999, of fever lasting > or = 3 days and one other symptom. Salmonella Typhi was isolated from 19 (38%) cases. Thirty-two (64%) patients were school-aged children, and 17 (34%) were in four households. Case-control studies of (a) culture-confirmed cases and age- and neighbourhood-matched controls; and (b) household index cases and randomly selected age-matched controls implicated two restaurants: Restaurant M (matched OR [MOR] = 11, 95% confidence interval [CI] = 1.3-96) and Restaurant I (MOR = 5.8, 95% CI = 1.2-29). Food-handlers at both restaurants had elevated anti-Vi antibody titres indicative of carrier state. The annual incidence was 5.0/1000 persons. Outbreak-associated costs were $46,000. Routine or emergency immunization campaigns targeting school-aged children may help prevent or control outbreaks of typhoid fever in endemic disease areas.     

Plasmid analysis as an epidemiological tool in neurosurgical infections with coagulase-negative staphylococci

Coagulase-negative staphylococci isolated from blood or spinal fluid during a period of 1 year in a department of neurosurgery, were analysed by biotyping, antibiotic resistance pattern and plasmid profiles. Altogether 41 isolates from 19 patients were studied. About 90% of the isolates were Staphylococcus epidermidis. The antibiotic resistance pattern seemed to be closely related to antibiotic usage in the unit. Most common was resistance to penicillin (63%), trimethoprim-sulphamethoxazole (49%) and cloxacillin (39%) while resistance to gentamicin was seen in only one strain. In several cases species and antibiograms were identical in isolates from different patients. Plasmid pattern analysis could then be used for identification of different strains. In one instance, plasmid pattern and restriction enzyme analysis confirmed that two patients probably were infected by the same strain.     

Sero-epidemiology as a tool to study the incidence of Salmonella infections in humans

Although most foodborne infections are undiagnosed, the incidence of these infections is usually calculated from reported cases. We present a novel population-based method to estimate the incidence of non-typhoid Salmonella infections. From 154 patients with confirmed Salmonella serotype Enteritidis infection, we determined the kinetics of the antibody response. The estimated mean responses for the three classes of serum antibodies were combined such that the time from infection could be estimated from antibody measurements. Next, serum samples collected in 1983, 1986, 1992, and 1999 from the general population were analysed for antibodies. We demonstrated how these measurements can be translated into an estimate of the general incidence. Based on serology markers there were 13 exposures leading to seroresponse of Salmonella Enteritidis/1000 person-years in 1983; the similar number in 1999 was 217. This trend confirms the increase in the number of culture-confirmed cases reported to the national surveillance system.     

Genome fingerprinting of Salmonella typhi by pulsed-field gel electrophoresis for subtyping common phage types.

The genomic DNA of 39 strains of Salmonella typhi isolated from local residents and patients who had visited countries in the Asian region was analysed for restriction fragment length polymorphisms (RFLP). Pulsed-field gel electrophoretic (PFGE) analysis of Xba I- and Spe I-generated genomic restriction fragments established 22 PFGE types whereas phage typing differentiated the 39 isolates into 9 distinct phage types. This study showed that PFGE is more discriminatory than phage typing as it is capable of subtyping S. typhi strains of the same phage types. Genetic relatedness among the isolates was determined. Seven major clusters were identified at SABs of > 0.80 and the remaining 13 isolates were distributed into minor clusters which were related at SABs of less than 0.80. In conclusion, PFGE analysis in conjunction with distance matrix analysis served as a useful tool for delineating common S. typhi phage types of diverse origins from different geographical locales and separated in time.     

Auxotrophic Salmonella typhi as live vaccine

Salmonella typhi 541Ty has deletions at aroA and purA, causing requirement for aromatic metabolites (including p-aminobenzoate) and for adenine. None of 36 volunteers who drank 10(8) to 10(10) bacteria of 541Ty or its Vi-negative mutant 543Ty showed any adverse effect; all gave evidence of cellular immune response but only a few had serum titre increases. S. typhimurium experiments (at the Wellcome Research Laboratories and at Stanford) show that adenine requirement may reduce both bacterial survival in mouse tissues and live-vaccine efficacy. S. typhi attenuated only by block(s) in aromatic biosynthesis may be more effective as oral-route live vaccine.     

Spread of Salmonella typhi in a maternity hospital.

An Asian patient with undiagnosed typhoid fever was admitted to a maternity hospital and delivered within 10 min. Salmonella typhi (phage type D5) was isolated from her blood and from the faeces of her baby. Another women in a different room of the labour suite at the same time acquired the same organism in her faeces; her brother was admitted to the Infectious Diseases Unit 5 weeks later with typhoid fever. Two babies, born over 60 h after the index case was delivered, became faecal excreters of the same strain and one of them also developed S. typhi osteitis of the hip. These two babies and their mothers were in the same ward as each other, but not that occupied by the infected mother and her baby. Nine other excreters in two of the families involved were identified. The index case and her baby were isolated immediately after delivery, and the relevant rooms in the labour suite were adequately disinfected. No evidence of undisinfected equipment used by the index case and the other infected patients was found, and no spread to staff was detected. The mode of spread remains unknown.     

The analysis of recurrence risk as an epidemiological tool

Recurrence risk provides information on the heterogeneity of risk in the population, and thus is useful for aetiological studies. While recurrence risk is observable in many areas of epidemiology, it is particularly accessible in the study of perinatal events. High recurrence rates of pregnancy problems suggest genetic causes, but can also reflect the presence of persistent environmental causes. Specific patterns of recurrence risk can provide further clues about the relative importance of genetic vs. environmental factors, for example through comparisons of recurring pregnancy problems in women who change their male partner and women who keep the same partner. Interpretation of recurrence risk is subject to confusion from bias and confounding, and some examples are discussed. In addition to providing information on causality, recurrence risk offers a means for more efficient design of aetiological studies.     

Phage typing and PFGE pattern analysis as tools for epidemiological surveillance of Salmonella enterica serovar Bovismorbificans infections

Some years ago, an increase in the number of sporadic cases and outbreaks of salmonellosis due to S. enterica serovar Bovismorbificans was observed in several European countries including Finland, Sweden, England/Wales, Austria, and Germany. In order to understand the recent spread of this serovar and to trace the route of infection back to its source, it was considered necessary to subtype S. Bovismorbificans isolates. Using phage typing (newly described here) and molecular fingerprinting (PFGE-pattern, plasmid profiles and ribotype) the isolates of European origin could be subtyped and compared to S. Bovismorbificans isolates that originated in overseas countries such as Australia, Thailand, India, etc. where this serovar was isolated more frequently. Significant clonal diversity was identified but some of the clonal types of S. Bovismorbificans dominated the epidemics and single cases in Europe as well as in overseas countries. The clonal identity among these isolates indicates an international distribution, new sources of infection, and highlights the urgent requirement for standardized laboratory based surveillance networks (e.g. Enter-Net). Moreover, it is suggested that strains of S. Bovismorbificans will continue to be of concern in public health and that phage typing together with PFGE typing can be applied as reliable and rapid tools for their future monitoring.     

贵州省伤寒沙门菌分离株16s核糖体基因型的多态性及其流行病学意义

目的：探讨贵州省不同时间、不同地区伤寒流行菌株的遗传多态性及内在联系。方法：利用southern杂交技术，对贵州省9个地区26个县、市1959－1999年伤寒沙门菌分离株进行染色体DNA基因限制性酶切16s rDNA探针杂交图谱分析及药物敏感性试验。结果：分析发现选择的209株分属26个RT型，以RT1和RT2为优势型；在局部发生伤寒流行时，均由独特的RT型引起。耐药菌株以RT7和RT1型为主。结论：贵州省不同地区、不同时间的分离菌株在核糖体杂交图谱上有明显的多态性，分析认为具有多重耐药性以及存在众多克隆群菌株是引起贵州伤寒发病率居高不下的主要原因。     

Genotypic analysis of multidrug-resistant Salmonella enterica Serovar typhi, Kenya

We report the emergence in Kenya during 1997-1999 of typhoid fever due to Salmonella enterica serovar Typhi resistant to ampicillin, tetracycline, chloramphenicol, streptomycin, and cotrimoxazole. Genotyping by pulsed-field gel electrophoresis of XbaI-digested chromosomal DNA yielded a single cluster. The multidrug-resistant S. Typhi were related to earlier drug- susceptible isolates but were unrelated to multidrug-resistant isolates from Asia.     

The dienes effect as an epidemiological tool in a paraplegic unit

The authors study the Dienes effect in 136 P. mirabilis and 2 P. vulgaris strains, isolated from different infection or colonization sites, in 27 spinal cord injured patients, admitted to a Paraplegic Unit, during a 9 month period. It is shown that 7 cross-infection and 18 cross-contamination episodes occurred, affecting 13 of 27 patients, which indicates the great spreading capacity of these microorganisms; 97% of the results obtained were observed once again after 6 months' storage of strains. In addition, in 7 of these strains their resistance to several antibiotics was cured by treating them with acriflavine salts, demostrating that the Dienes effect persists even when resistance to antibiotics is modified; the authors conclude that the Dienes effect is an accurate stable epidemiological tool to identify cross-infections and its origins, and to facilitate the interruption of the chain of infection.Corresponding author.