Interregional foodborne salmonellosis outbreak due to powdered infant formula contaminated with lactose-fermenting Salmonella virchow

Validation of process technologies for enhancing the safety of low-moisture foods: A review

The outbreaks linked to foodborne illnesses in low-moisture foods are frequently reported due to the occurrence of pathogenic microorganisms such as Salmonella Spp. Bacillus cereus, Clostridium spp., Cronobacter sakazakii, Escherichia coli, and Staphylococcus aureus. The ability of the pathogens to withstand the dry conditions and to develop resistance to heat is regarded as the major concern for the food industry dealing with low-moisture foods. In this regard, the present review is aimed to discuss the importance and the use of novel thermal and nonthermal technologies such as radiofrequency, steam pasteurization, plasma, and gaseous technologies for decontamination of foodborne pathogens in low-moisture foods and their microbial inactivation mechanisms. The review also summarizes the various sources of contamination and the factors influencing the survival and thermal resistance of pathogenic microorganisms in low-moisture foods. The literature survey indicated that the nonthermal techniques such as CO₂ , high-pressure processing, and so on, may not offer effective microbial inactivation in low-moisture foods due to their insufficient moisture content. On the other hand, gases can penetrate deep inside the commodities and pores due to their higher diffusion properties and are regarded to have an advantage over thermal and other nonthermal processes. Further research is required to evaluate newer intervention strategies and combination treatments to enhance the microbial inactivation in low-moisture foods without significantly altering their organoleptic and nutritional quality.

Labchip-based diagnosis system for on-site application: Sensitive and easy-to-implement detection of single recoverable Cronobacter in infant formula without post-enrichment treatment

Microfluidic labchips have achieved much advancement in the molecular diagnosis of foodborne pathogens. Whereas difficulties in the flow control during the transportation of liquid fluids can occur and should be overcome. Manipulations of reaction temperature and the complex procedures from sample pre-treatment to analysis in a single chip device are major obstacles for the on-site application. Thus, the efficient temperature control of samples without any flow of reaction fluids in microfluidic channels of plastic chip and the simplest protocol omitting post-enrichment processing steps may overcome these limitations represented by the stability and the complexity, respectively. This study aims to develop a novel type of labchip and thermocycler specialized for the gene amplification in microfluidic channels and to evaluate the detectability by sensing the minimum recoverable level of Cronobacter in powdered infant formula (PIF). We developed a thermocycling device accelerating reactions through dual heating-blocks optimized to control temperatures of samples in microfluidic-channels by direct contact with labchip sequentially and repetitively. The structural design of microfluidic channels was to eliminate interference factors associated with the optical detection of fluorescent signals (without distortion due to air bubbles in the reaction chamber). To improve the applicability, a portable device and simplified operation to allow direct loading of samples in the chip without post-enrichment procedures were also adopted. Detection performance was evaluated by a sensitivity/specificity tests using 50 isolates of Cronobacter. Cross-reactivity tests for non-Cronobacter organisms and gDNA [human, raw materials of PIF (cow, soybean)] showed that there was no interference-factor causing false-positive results. In terms of the applied research conducted by using PIF, the enrichment of samples without broth medium (distilled water) displayed outstanding performance and 12 h of incubation facilitated detecting target at concentration as low as 1 CFU/300 g PIF (as initial contamination level) without post-enrichment treatment. Validation of the operation conditions using 30 commercial PIF products was also consistent. The present study presents a novel approach of microfluidic technology with perspective to not only the performance and the practicability [easy-to-implement protocol, portable materials, cost-effectiveness (the use of a miniaturized plastic chip requires a minimum level of materials)] for on-site diagnosis.

The risk of infectious pathogens in breast-feeding, donated human milk and breast milk substitutes

OBJECTIVE

This review collates the published reports that focus on microbial and viral illnesses that can be transmitted by breast milk, donor milk and powdered infant formula (PIF). In this context, we attempt to define a risk framework encompassing those hazards, exposure scenarios, vulnerability and protective factors.

DESIGN

A literature search was performed for reported cases of morbidity and mortality associated with different infant feeding modes.

SETTING

Exclusive breast-feeding is the recommended for infant feeding under 6 months, or failing that, provision of donated human milk. However, the use of PIF remains high despite its intrinsic and extrinsic risk of microbial contamination, as well as the potential for adverse physiological effects, including infant gut dysbiosis.

RESULTS

Viable pathogen transmission via breast-feeding or donor milk (pasteurised and unpasteurised) is rare. However, transmission of HIV and human T-cell lymphotropic virus-1 is a concern for breast-feeding mothers, particularly for mothers undertaking a mixed feeding mode (PIF and breast-feeding). In PIF, intrinsic and extrinsic microbial contamination, such as Cronobacter and Salmonella, remain significant identifiable causes of infant morbidity and mortality.

CONCLUSIONS

Disease transmission through breast-feeding or donor human milk is rare, most likely owing to its complex intrinsically protective composition of human milk and protection of the infant gut lining. Contamination of PIF and the morbidity associated with this is likely underappreciated in terms of community risk. A better system of safe donor milk sharing that also establishes security of supply for non-hospitalised healthy infants in need of breast milk would reduce the reliance on PIF.

Ongoing nationwide outbreak of Salmonella Agona associated with internationally distributed infant milk products, France, December 2017

On 1 December 2017, an outbreak of Salmonella Agona infections among infants was identified in France. To date, 37 cases (median age: 4 months) and two further international cases have been confirmed. Five different infant milk products manufactured at one facility were implicated. On 2 and 10 December, the company recalled the implicated products; on 22 December, all products processed at the facility since February 2017. Trace-forward investigations indicated product distribution to 66 countries.

Riscos microbiológicos de fórmulas para lactentes

Resumo O objetivo desse trabalho foi discorrer sobre os principais perigos biológicos encontrados em fórmulas infantis a partir dos relatos da literatura, especialmente de registros de surtos. Este estudo é de cunho exploratório por meio de revisão bibliográfica, sendo utilizados como fontes de dados sites de busca científica. Dentre os principais micro-organismos causadores de doenças ligadas à ingestão de fórmulas infantis estão o Cronobacter sakazakii e a Salmonella enterica, porém outras bactérias, como Clostridium botulinum, Klebsiella pneumoniae, Staphylococcus aureus e Bacillus cereus, podem ser responsáveis por contaminações destas fórmulas. Visto que lactentes apresentam os sistemas imunológico e metabólico ainda em desenvolvimento, estes representam um público mais vulnerável a contaminantes, fazendo-se fundamental o oferecimento de alimentos seguros desde o processamento na indústria até a administração nas residências e unidades hospitalares.

Associations of Salmonella hospitalizations with ambient temperature, humidity and rainfall in Hong Kong

BACKGROUND

Little is known about the relationship between Salmonella infection and meteorological parameters other than air temperature. This study aimed to explore associations of Salmonella hospitalizations with temperature, relative humidity (RH) and rainfall.

METHODS

With negative binomial distribution assumed, time-series regression model adjusting for season and time trend were constructed employing distributed lag non-linear models and generalized additive models. Meteorological variables including mean temperature, RH, and daily total rainfall as well as indicator variables including day of the week and public holiday were incorporated in the models.

RESULTS

Higher temperature was strongly associated with more hospitalizations over the entire range of temperatures observed. There was a net 6.13 (95%Confidence Interval (CI) 3.52-10.67) relative risk of hospitalization at a temperature of 30.5 °C, relative to 13 °C, lag 0-16 days. Positive associations were found for RH above 60% and rainfall between 0 and 0.14 mm. Extreme high humidity (96%) and trace rainfall (0.02 mm) were associated with 2.06 (95%CI 1.35-3.14), lag 0-17 day, and 1.30 (95%CI 1.01-1.67), lag 0-26 days, relative risks of hospitalizations, relative to 60% and no rain, respectively.

CONCLUSIONS

High temperatures, high RH and light rainfall are positively associated with Salmonella hospitalizations. The very strong association with temperatures implies that hotter days will lead to increases in Salmonella morbidity in the absence of other changes, and the public health implications of this could be exacerbated by global climate change.

Dehydrated foods: Are they microbiologically safe?

Dried foods are low water activity foods with water activity ranging from 0.03 to 0.7. They are commonly misconstrued to be inherently safe from food borne pathogenic bacteria. However, there are many reported cases where many food borne illnesses were caused by the consumption of dried foods contaminated with Salmonella spp., Cronobacter spp., Staphylococcus spp. and E. coli. In this work, we have systematically reviewed the literature dealing with the effect of drying/dehydration on the survival of pathogenic microorganisms with special focus on Salmonella spp. We have also reviewed and synthesized the literature dealing with the effect of drying process on microorganisms in dried vegetables, meat, fish, spices, mushroom and powdered foods. This review concludes that dried foods are not inherently safe microbiologically and required other hurdles to achieve microbial safety.

The response of foodborne pathogens to osmotic and desiccation stresses in the food chain

In combination with other strategies, hyperosmolarity and desiccation are frequently used by the food processing industry as a means to prevent bacterial proliferation, and particularly that of foodborne pathogens, in food products. However, it is increasingly observed that bacteria, including human pathogens, encode mechanisms to survive and withstand these stresses. This review provides an overview of the mechanisms employed by Salmonella spp., Shiga toxin producing E. coli, Cronobacter spp., Listeria monocytogenes and Campylobacter spp. to tolerate osmotic and desiccation stresses and identifies gaps in knowledge which need to be addressed to ensure the safety of low water activity and desiccated food products.

Prevalence and characterization of Salmonella enterica in dried milk-related infant foods in Shaanxi, China

The aim of this study was to investigate the existence and characteristics of Salmonella enterica in dried milk-related infant foods. Twenty-four (3.4%) of 705 samples, including 5 (2.0%) of 246 powdered infant formula, 18 (4.0%) of 445 infant rice cereal, and 1 (7.1%) of 14 other infant foods, were positive for Salmonella. Fifteen serotypes were identified in 40 Salmonella isolates; Salmonella Duesseldorf (15.0%) and Salmonella Indiana (15.0%) were more frequently detected than other serotypes. Resistance to chloramphenicol (82.5%) was most common, followed by tetracycline (57.5%), ceftiofur (52.5%), kanamycin (52.5%), streptomycin (50.0%), gentamycin (45.0%), nalidixic acid (35.0%), ceftriaxone (32.5%), ciprofloxacin (25.0%), amikacin (20.0%), and cefoxitin (15.0%). Twenty-eight (70.0%) isolates were resistant to ≥ 8 antimicrobials, with 5 (12.5%) being resistant to 14 antimicrobials. Amino acid substitutions in gyrase A (GyrA) were most frequently detected as Ser83Arg/Asp87Glu and in p53-associated Parkin-like cytoplasmic protein (ParC), they were all Ser80Arg; the quinolone resistance gene qnrS (47.5%) was commonly detected as well as aminoglycoside acetyltransferase [aac(6')-Ib; 25.0%], qnrA (17.5%), and qnrB (15.0%) genes. Thirty distinct pulsed-field gel electrophoresis patterns were identified among 40 isolates; no identical pulsed-field gel electrophoresis pattern was detected among Salmonella isolates with the same serovar that was recovered in 2010 and 2012. Our results suggest that dried milk-related infant foods could be contaminated with Salmonella and highlight that the dangers to infant health should not be neglected.

Genetic characterization of atypical Citrobacter freundii

The ability of a bacterial population to survive in different niches, as well as in stressful and rapidly changing environmental conditions, depends greatly on its genetic content. To survive such fluctuating conditions, bacteria have evolved different mechanisms to modulate phenotypic variations and related strategies to produce high levels of genetic diversity. Laboratories working in microbiological diagnosis have shown that Citrobacter freundii is very versatile in its colony morphology, as well as in its biochemical, antigenic and pathogenic behaviours. This phenotypic versatility has made C. freundii difficult to identify and it is frequently confused with both Salmonella enterica and Escherichia coli. In order to determine the genomic events and to explain the mechanisms involved in this plasticity, six C. freundii isolates were selected from a phenotypic variation study. An I-CeuI genomic cleavage map was created and eight housekeeping genes, including 16S rRNA, were sequenced. In general, the results showed a range of both phenotypes and genotypes among the isolates with some revealing a greater similarity to C. freundii and some to S. enterica, while others were identified as phenotypic and genotypic intermediary states between the two species. The occurrence of these events in natural populations may have important implications for genomic diversification in bacterial evolution, especially when considering bacterial species boundaries. In addition, such events may have a profound impact on medical science in terms of treatment, course and outcomes of infectious diseases, evading the immune response, and understanding host-pathogen interactions.

Risk factors for salmonella gastroenteritis in children less than five years of age in Taiwan

BACKGROUND

Nontyphoid Salmonella spp. have been among the most common pathogens of acute gastroenteritis in children in Taiwan. However, the principal sources of transmission remain poorly defined.

METHODS

A matched case-control study was conducted from January 2009 to October 2010. Cases were children aged 2-60 months who were hospitalized at 3 medical centers in Taiwan because of diarrhea and found to have culture-proven nontyphoidal Salmonella infection. Controls were healthy children or children with acute diseases other than gastroenteritis and matched to cases by age, gender, study site and enrollment date.

RESULTS

A total of 396 cases and 930 matched controls were included for analysis. Multivariate analysis using conditional logistic regression identified contact with household members having diarrhea (matched odds ratio [mOR], 17.9; 95% confidence interval [CI]: 8.82-36.34; P < 0.0001), consumption of instant powdered milk (mOR, 2.04; 95% CI: 1.05-3.94; P = 0.0344), visits to health-care facilities (mOR, 1.66; 95% CI: 1.12-2.48; P = 0.0126) and consumption of purchased groundwater (mOR, 1.50; 95% CI: 1.06-2.11; P = 0.0214) within 1 week preceding enrollment as independent factors associated with increased risk of salmonellosis. Hand washing before meals (P = 0.0311), breastfeeding (P = 0.0370), consumption of chicken (P = 0.0019) and consumption of food prepared by caregivers (P = 0.0011) were protective against Salmonella infection.

CONCLUSIONS

The principal transmission routes of Salmonella infection in Taiwanese children are person-to-person, waterborne and environmental contacts. The possibility of powdered milk and groundwater contamination of Salmonella cannot be excluded and requires further investigation.

Survival of Salmonella on a polypropylene surface under dry conditions in relation to biofilm-formation capability

This study was conducted to gain insights into the survival of Salmonella on a polypropylene surface in relation to the ability of these bacteria to form a biofilm. We selected Salmonella strains known for the relative ease or difficulty with which they formed biofilms based on microtiter plate assays and studied the survival of these strains on polypropylene discs in a desiccation chamber by sequentially counting CFUs. The biofilm-forming strains survived longer on the plastic disc surface than did biofilm-deficient strains. The biofilm-forming strains remained at over 10(4) CFU per plate until day 175, whereas the biofilm-deficient strains decreased to below 10(2) CFU per plate on day 20 or below 10(4) CFU per plate on day 108. Extracellular materials on the polypropylene surface were observed by scanning electron microscopy and crystal violet staining for the biofilm-forming strains but not for the biofilm-deficient strains. The extracellular polymeric materials on the polypropylene surface may have protected the bacterial cells from dryness, although the possibility of some inherent resistance to environmental stresses linked to biofilm formation could not be excluded. These results indicate that Salmonella strains with high biofilm productivity may be a greater risk to human health via food contamination by surviving for longer periods compared with strains with low biofilm productivity.

A survey on knowledge and self-reported formula handling practices of parents and child care workers in Palermo, Italy

BACKGROUND

Powdered infant formula (PIF) is not a sterile product, but this information appears to be poorly diffused among child caregivers. Parents and child care workers may behave in an unsafe manner when handling PIF.

METHODS

This study involved parents and child care workers in the 24 municipal child care centres of Palermo. Knowledge and self-reported practices about PIF handling were investigated by a structured questionnaire. A Likert scale was used to measure the strength of the respondent's feelings. Association of knowledge and self-reported practices with demographic variables was also evaluated.

RESULTS

42.4% of parents and 71.0% of child care workers filled in the questionnaire. Significant differences were found between parents and child care workers for age and education. 73.2% of parents and 84.4% of child care workers were confident in sterility of PIF. Generally, adherence to safe procedures when reconstituting and handling PIF was more frequently reported by child care workers who, according to the existing legislation, are regularly subjected to a periodic training on food safety principles and practices. Age and education significantly influenced the answers to the questionnaire of both parents and child care workers.

CONCLUSION

The results of the study reveal that parents and child care workers are generally unaware that powdered formulas may contain viable microorganisms. However, child care workers consistently chose safer options than parents when answering the questions about adherence to hygienic practices.At present it seems unfeasible to produce sterile PIF, but the risk of growth of hazardous organisms in formula at the time of administration should be minimized by promoting safer behaviours among caregivers to infants in both institutional settings and home.

Development and application of a novel peptide nucleic acid probe for the specific detection of Cronobacter genomospecies (Enterobacter sakazakii) in powdered infant formula

Here, we report a fluorescence in situ hybridization (FISH) method for rapid detection of Cronobacter strains in powdered infant formula (PIF) using a novel peptide nucleic acid (PNA) probe. Laboratory tests with several Enterobacteriaceae species showed that the specificity and sensitivity of the method were 100%. FISH using PNA could detect as few as 1 CFU per 10 g of Cronobacter in PIF after an 8-h enrichment step, even in a mixed population containing bacterial contaminants.

The importance of hygiene in the domestic kitchen: Implications for preparation and storage of food and infant formula

Aims: Public concerns relating to food safety remain high with most attention focused on manufactured foods and those served in catering operations. However, previous data have suggested that the home may be the main location for cases of food-borne disease. The aim of this paper is to review the microbiological risks associated with hygiene in the domestic kitchen related to food and infant formula safety.

Methods: Compared to other food sectors, research on consumer food hygiene, domestic food-handling and preparation of infant formula is relatively understudied. Behavioural and microbiological studies of consumer hygiene and the domestic kitchen have been reviewed to incorporate research relating to the safety of infant formula.

Results: Incidence data identify the home as an important location for acquiring food-borne disease. The domestic kitchen can be used for a variety of purposes and is often contaminated with potentially harmful micro-organisms such as Campylobacter and Salmonella. Consumer hygiene habits have frequently been found to be inadequate and relate both to microbial growth, survival and cross-contamination. Due to the reduced immune response of infants, the activities associated with the preparation of infant formula and associated bottles and equipment are of particular concern.

Conclusions: Cumulatively, the data suggest that more effort should be made to educate the consumer in food hygiene, especially when the kitchen is used to reconstitute infant formula. This information needs to be provided in a form appropriate for use by consumers.

Powdered infant formula as a source of Salmonella infection in infants

Powdered infant formula is not sterile and may be intrinsically contaminated with pathogens, such as Salmonella enterica, that can cause serious illness in infants. In recent years, at least 6 outbreaks of Salmonella infection in infants that have been linked to the consumption of powdered infant formula have been reported. Many of these outbreaks were identified because the Salmonella strains were unique in some way (e.g., a rare serotype) and a well-established Salmonella surveillance network, supported by laboratories capable of serotyping isolates, was in place. Another common feature of the outbreaks was the low level of salmonellae detected in the implicated formula (salmonellae may be missed in routine testing). These outbreaks likely represent only a small proportion of the actual number of Salmonella infections in infants that have been linked to powdered infant formula. Managing this problem requires a multidimensional approach in which manufacturers, regulators, and caregivers to infants can all play a role.

Brote de gastroenteritis en una guardería causado por una cepa de Salmonella enterica serovar Typhimurium portadora del plásmido híbrido de resistencia-virulencia pUO-StVR2

OBJECTIVE

Epidemiological and microbiological study of a salmonellosis outbreak, affecting 22 children in a nursery school in Oviedo (Spain).

METHODS

Attack rates and epidemic curves were determined, and bacterial typing methods were applied.

RESULTS

The outbreak was attributed to a Salmonella enterica serovar Typhimurium strain, belonging to an emergent type characterized by the presence of a hybrid virulence-resistance plasmid of 125-130 kb, named pUO-StVR2. The attack rate of confirmed cases vs. possible cases was 27.2% vs. 23.5% for the children and 0 vs. 26.5% for the staff of the affected center. The source of the infection could not be identified. Nevertheless, according to the evolution of the cases over time, the transmission route was likely to be personal contact between the staff and children, which facilitates fecal-oral dissemination. All but one of the 27 isolates analyzed (from 22 patients) showed identical features: R-profile, plasmid-profile, RAPD-type, PFGE-type; all were non-phage-typeable, with the exception of a DT104b isolate. pUO-StVR2 is probably a derivative of the virulence plasmid pSLT from the LT2 type strain that acquired an R-region complex (ACSSuT/blaOXA-catA1-strA/ B-aadA1-sul1-sul2-tet[B]), in which the blaOXA-aadA1 genes are part of the variable region of a class 1 integron.

CONCLUSION

This outbreak is an example of how a Salmonella enterica serovar Typhimurium strain belonging to a type that is probably endemic in Spain can be transferred to the community and affect a susceptible population.

Two consecutive large outbreaks of Salmonella enterica serotype Agona infections in infants linked to the consumption of powdered infant formula

BACKGROUND

An increase of isolation of Salmonella Agona was observed in January through February 2005 among infants in France.

METHODS

Case-control study, food trace-back and microbiologic investigations were promptly carried out.

RESULTS

A total of 141 confirmed cases <12 months of age were identified. Most had diarrhea (99%; bloody 56%) and fever (75%) and 36% were hospitalized for 5 days on average and none died. In the case-control analysis, all 23 cases and none of the 23 controls had consumed powdered formula of brand A (P < 10(-5)). Active follow up of all cases showed that after the withdrawal of formula A, cases that had consumed formula A decreased rapidly, but new cases had consumed another formula (brand B). The trace-back found that 5 batches of formula B had been manufactured on the same production line as formula A. Forty-four cases were linked to formula A and 92 to formula B. All routine controls performed by the producers were negative for Salmonella. However, enhanced microbiologic investigations yielded S. Agona in one of 176 samples of formula A, in 4 of 27 tins of formula B consumed by cases and in 6 of 420 environmental swabs from the production line. All clinical, food and environmental isolates were of the same pulsed-field gel electrophoresis profile.

CONCLUSIONS

Powdered infant formulas are not sterile products and may contain low levels of Salmonella. Routine microbiologic controls are insufficient to detect a low-grade contamination, which may cause serious illness and outbreaks among infants.

Salmonella enterica serotype Virchow: epidemiology, resistance patterns and molecular characterisation of an invasive Salmonella serotype in Israel

This study outlines the unique epidemiology of Salmonella enterica serotype Virchow in Israel. Between 1997 and 2002, the overall incidence of non-typhoid Salmonella enterica (NTS) decreased from 69.3 to 53.3 infections/100,000 population, but the incidence of S. Virchow increased (from 7.2 to 9.1 infections/100,000). Since 2000, S. Virchow has become the second-ranking NTS isolate, accounting for 17% and 27% of all stool and blood NTS isolates, respectively. Infants aged < 1 year had the highest incidence of isolation from stools (92.8/100,000). The incidence of isolation from blood was highest for infants aged <1 year (4.4/100,000). Only 6% of isolates were susceptible to all ten antibiotic agents tested; 34% were resistant to one agent, 54% to one to three agents, and 40% to four to six agents. A high proportion of the tested isolates were resistant to nalidixic acid (89%), streptomycin (56%), tetracycline (43%), trimethoprim-sulphamethoxazole (38%) and chloramphenicol (28%), but none to ciprofloxacin or ceftriaxone. Pulsed-field gel electrophoresis revealed two closely related clusters, each containing a predominant pulsotype. Coupled with its invasive propensity, the increasing incidence of highly resistant S. Virchow in Israel is of real concern. Future research should focus on the sources of S. Virchow in the food chain in order to institute effective control measures.

A case-control study of the epidemiology of sporadic Salmonella infection in infants

OBJECTIVE

Rates of Salmonella infection are highest in infants, but little is known about potential sources of infection in this high-risk population. We performed a case-control study to identify dietary and environmental risk factors for sporadic salmonellosis among infants.

PATIENTS AND METHODS

In 2002-2004, the Foodborne Diseases Active Surveillance Network conducted a population-based, case-control study of sporadic salmonellosis among infants <1 year of age in 8 states. Cases were identified via active laboratory-based surveillance. Healthy controls were frequency matched by age and identified through birth registries or published birth announcements. We assessed diet and environmental exposures in the 5 days before illness onset or interview. Data were analyzed by using logistic regression adjusting for age.

RESULTS

The study enrolled 442 subjects and 928 controls. Compared with healthy controls, infants with Salmonella infection were less likely to have been breastfed and more likely to have had exposure to reptiles, to have ridden in a shopping cart next to meat or poultry, or to have consumed concentrated liquid infant formula during the 5-day exposure period. Travel outside the United States was associated with illness in infants 3 to 6 and >6 months of age. Attending day care with a child with diarrhea was associated with salmonellosis in infants >6 months of age.

CONCLUSIONS

We identified a number of modifiable protective and risk factors for salmonellosis in infants. Attention should be directed at developing effective preventive measures for this high-risk population.

Invasive Enterobacter sakazakii disease in infants

Enterobacter sakazakii kills 40%–80% of infected infants and has been associated with powdered formula. We analyzed 46 cases of invasive infant E. sakazakii infection to define risk factors and guide prevention and treatment. Twelve infants had bacteremia, 33 had meningitis, and 1 had a urinary tract infection. Compared with infants with isolated bacteremia, infants with meningitis had greater birthweight (2,454 g vs. 850 g, p = 0.002) and gestational age (37 weeks vs. 27.8 weeks, p = 0.02), and infection developed at a younger age (6 days vs. 35 days, p<0.001). Among meningitis patients, 11 (33%) had seizures, 7 (21%) had brain abscess, and 14 (42%) died. Twenty-four (92%) of 26 infants with feeding patterns specified were fed powdered formula. Formula samples associated with 15 (68%) of 22 cases yielded E. sakazakii; in 13 cases, clinical and formula strains were indistinguishable. Further clarification of clinical risk factors and improved powdered formula safety is needed.

Enterobacter sakazakii: an emerging pathogen in powdered infant formula

Enterobacter sakazakii represents a significant risk to the health of neonates. This bacterium is an emerging opportunistic pathogen that is associated with rare but life-threatening cases of meningitis, necrotizing enterocolitis, and sepsis in premature and full-term infants. Infants aged <28 days are considered to be most at risk. Feeding with powdered infant formula (PIF) has been epidemiologically implicated in several clinical cases. Infants should be exclusively breast-fed for the first 6 months of life, and those who are not should be provided with a suitable breast-milk substitute. PIF is not a sterile product; to reduce the risk of infection, the reconstitution of powdered formula should be undertaken by caregivers using good hygienic measures and in accordance with the product manufacturer's food safety guidelines.

[Salmonellosis in a maternity-children's hospital in Barcelona over a 10-year period (1992-2001)]

BACKGROUND

We performed a retrospective study of Salmonella spp. strains, as well as of serotypes and resistance to antimicrobial agents that could be useful in salmonellosis requiring antibiotic treatment.

MATERIAL AND METHODS

All Salmonella strains isolated in a maternity-children's hospital in Barcelona (Spain) during a 10-year period (1992-2001) were serotyped. The susceptibility of the strains isolated from 1994 to ampicillin, amoxicillin-clavulanic acid, chloramphenicol, trimethoprim-sulfamethoxazole and cefotaxime was analyzed. Ciprofloxacin substituted chloramphenicol in the analysis of strains isolated during the last 2 years of the study period.

RESULTS AND DISCUSSION

A total of 860 isolates from 31 distinct serotypes were analyzed. The most frequent serotypes were S. enteritidis (48.7 %), S. typhimurium (33.4 %), S. virchow (5 %), S. hadar (1.8 %) and S. typhi (1.5 %). We found a high percentage of strains resistant to ampicillin (44.6 % in 2001) and chloramphenicol (28.7 % in 1999) and a lower percentage of strains resistant to amoxicillin-clavulanic acid and trimethoprim-sulfamethoxazole (2.2 % and 6.5 % respectively, among the strains isolated in 2001). Only one cefotaxime-resistant strain was found, and all isolates were susceptible to ciprofloxacin. Our results provide useful epidemiological information for the control of these infections, which remain a serious public health problem all over the world.

A collaborative study to evaluate qualitatively powdered baby food validation samples artificially contaminated with Salmonella anatum

Nineteen laboratories participated in a collaborative study to evaluate the performance of validation samples consisting of powdered infant formula and cereal-based weaning food artificially contaminated with low levels of Salmonella anatum. The Standard method BS EN ISO 6579:2002 was to be followed for the trial. Salmonella counts in each baby food were around 10 CFU/25 g (low) or 10 CFU/g (high level). Trial participants received five samples of each sample type and five blank samples. All samples contained Pseudomonas aeruginosa and Lactobacillus spp. at concentrations between 10(4) and 10(5) CFU/g as background flora. Precision data for the powdered infant formula were similar for the solid selective plating-out medium xylose-lysine-deoxycholate (XLD) and a 2nd choice of agar suitable to isolate Salmonella spp. The sensitivity was 91.3%, accordance 82.5% and concordance 83.9% for the low and 100% for the high level in all cases. For the cereal-based weaning food, the precision data for the high level were similar for XLD and the 2nd choice medium (98.8%, 97.5% and 97.5%). A slight difference was observed for the low level where XLD obtained values of 82.5%, 73.8%, 70.6% for sensitivity, accordance and concordance and the second choice medium values of 81.5%, 72.5% and 69%. The specificity, accordance and concordance of blanks for the infant formula and cereal-based weaning food were 100%.

Usefulness of different techniques in the study of the epidemiology of salmonellosis

Our objective was to evaluate the usefulness of serotyping, phagotyping, antibiotyping and RAPD (random amplified polymorphic DNA) in the study of the epidemiology of salmonellosis in Elche (Spain). We examined 1232 clinical isolates of non-typhoid Salmonella serotypes. Serotyping adequately differentiates 12.3% of the isolates and phagotyping raises this percentage to 37%. Antibiotyping is a suitable complement in certain circumstances, such as in the case of specific outbreaks. RAPD is a fast and simple technique which is within the reach of most laboratories, complementing the results obtained by antibiotyping and serotyping, in order to be able to control outbreaks of salmonellosis in everyday practice.

Salmonella serotype Virchow causing salmonellosis in a Spanish region. Characterization and survey of clones by DNA fingerprinting, phage typing and antimicrobial resistance

The diversity of Salmonella serotype Virchow organisms causing human salmonellosis in a Spanish region over 1990-1996 was studied by genetic and phenotypic procedures. Isolates showing identical DNA fingerprintings (ribotypes, RAPD-, REP- and ERIC-types) were clustered into the same lineage. Eight lineages were defined, of which only one caused diseases throughout the studied period. Eleven phage types (PTs) were represented, the most frequent being PTs 8, 19, 31, throughout the study period, and PT4a only during 1994. Class I integrons with variable regions of 1000-, 1600-, and 2300-bp in size were respectively present in 24, 3 and 5 multiresistant isolates; 43.5% of isolates were susceptible to antimicrobials, the rest were grouped into 17 R-profiles, including from one up to eight resistances. Plasmids could be recovered from 71.5% of isolates and grouped into 25 plasmid profiles (with 1-7 plasmids each); a 3.6 kb cryptic-plasmid and a 60 kb virulence-plasmid were those most frequently found. Phage type, presence and size of integrons, and resistance profile were used to differentiate 39 clones. During the period studied 135 cases of Virchow salmonellosis were identified; 93 were apparently sporadic whereas the remainder were associated with four outbreaks. Infants under 1 year constituted the most frequent age group, with 30 gastroenteritis and two septicaemia episodes. In the four outbreaks, different clones falling into the prevalent lineage were implicated but each clone was involved in only one outbreak.

Implication of milk and milk products in food-borne diseases in France and in different industrialised countries

A study was carried out to estimate the proportion of diseases due to milk and milk products among food-borne diseases recorded in France and in other countries since 1980. Particular attention was given to whether the milk involved was heat-treated or not. Four etiologic agents were considered: Salmonella spp., Staphylococcus aureus, Listeria monocytogenes, and pathogenic Escherichia coli. An overview of food-borne disease annual reports from seven countries indicated that milk and milk products were implicated in 1-5% of the total bacterial outbreaks; however, details about the type of product and milk involved were usually not provided. When considering 60 outbreaks and four single cases described in the literature and implicating milk and milk products, confirmed or suspected food vehicles were distributed as follows: milk, 39.1%, cheese, 53.1%, other milk products, 7.8%. Overall, 32.8% of the food vehicles were made from pasteurised milk; 37.5% from raw milk; 10.9% from milk stated as "unpasteurised"; and 18.8% from unspecified milk. Salmonella spp. were responsible for 29 outbreaks, L. monocytogenes for 10 outbreaks and four well-documented single cases, pathogenic E. coli for 11 outbreaks, and S. aureus for 10 outbreaks. Analysis of unpublished data about food-borne disease outbreaks, listeriosis excluded, collected by the coordinator of the French surveillance system from 1992 to 1997, revealed 69 documented outbreaks for which milk and milk products were confirmed as the vehicle by the isolation of the etiologic agent. The food vehicles were distributed as follows: milk, 10%; cheese, 87%; others, 3%. UHT milk accounted for 1.5%, raw milk and raw milk products for 48%, and milk and milk products from unspecified milk for 50.5% of the 69 outbreaks. S. aureus was by far the most frequent pathogen associated with these outbreaks (85.5% of the outbreaks), followed by Salmonella (10.1%). This study demonstrates the limitations of the surveillance systems and the difficulties in estimating the contribution of milk and milk products to food-borne diseases. In particular, it was not possible to find out in many outbreaks what heat treatment, if any, the milk had undergone.

Incidence of Salmonella in fish and seafood

Field laboratories of the U.S. Food and Drug Administration collected and tested 11,312 import and 768 domestic seafood samples over a 9-year period (1990 to 1998) for the presence of Salmonella. The overall incidence of Salmonella was 7.2% for import and 1.3% for domestic seafood. Nearly 10% of import and 2.8% of domestic raw seafood were positive for Salmonella. The overall incidence of Salmonella in ready-to-eat seafood and shellfish eaten raw was 0.47% for domestic--one shucked oyster and one shark cartilage powder. The incidence in the 2,734 ready-to-eat import seafood was 2.6%--cooked shrimp, shellfish or fish paste, smoked fish, salted/dried fish, and caviar. The incidence in import shellfish consumed raw was 1% in oyster, 3.4% in clams, and 0% in mussels. The incidence in raw, import fish was 12.2%. Distribution of Salmonella in seafood on a regional basis indicated the incidence to be highest in central Pacific and Africa and lowest in Europe/Russia and North America (12% versus 1.6%). Data on a country basis indicated Vietnam to have the highest (30%) and Republic of Korea the lowest (0.7%). While the most frequent serotypes in import seafood were Salmonella Weltevreden (1st), Salmonella Senftenberg (2nd), Salmonella Lexington, and Salmonella Paratyphi-B (3rd, equal numbers for each serotype), the top 20 list included Salmonella enteritidis (5th), Salmonella Newport (6th), Salmonella Thompson (7th), Salmonella typhimurium (12th), and Salmonella anatum (13th), commonly involved in foodborne illness in the United States. Because the incidence in the present study is based on only a small fraction of the seafood imported into the United States, efforts should be directed toward implementation of hazard analysis and critical control points to reduce the incidence of Salmonella in seafood without relying on testing for Salmonella.

Diagnostic and public health dilemma of lactose-fermenting Salmonella enterica serotype Typhimurium in cattle in the Northeastern United States

The presence of lactose-fermenting Salmonella strains in clinical case materials presented to microbiology laboratories presents problems in detection and identification. Failure to detect these strains also presents a public health problem. The laboratory methods used in detecting lactose-fermenting Salmonella enterica serotype Typhimurium from six outbreaks of salmonellosis in veal calves are described. Each outbreak was caused by a multiply-resistant and lactose-fermenting strain of S. enterica serotype Typhimurium. The use of Levine eosin-methylene blue agar in combination with screening of suspect colonies for C8 esterase enzyme and inoculation of colonies into sulfide-indole-motility medium for hydrogen sulfide production was particularly effective for their detection. A hypothesis for the creation of lactose-fermenting salmonellae in the environment is presented. It is proposed that the environment and husbandry practices of veal-raising barns provide a unique niche in which lactose-fermenting salmonellae may arise.

Multiple analysis of a foodborne outbreak caused by infant formula contaminated by an atypical Salmonella virchow strain

An outbreak of food poisoning involving most autonomous Spanish communities was detected in the first half of 1994. The causative food was infant formula milk contaminated by lactose-fermenting Salmonella virchow. It was not possible to isolate the causative strain from the manufacturer's facilities. During the same period of time, there was a significant increase in lactose-non-fermenting Salmonella virchow strains compared with the same period in previous years. Simultaneously, lactose-non-fermenting strains were recovered from clinical samples from children and from some milk samples that were involved in the outbreak. Therefore, it was speculated that the outbreak might be more extensive than initially thought. The following epidemiological markers were used for typing the Salmonella virchow strains involved in the outbreak: (i) phage typing: (ii) ribotyping, using a set of 20 different endonucleases: and (iii) pulsed-field gel electrophoresis, using three different endonucleases. The most useful markers for this serotype were phage typing and pulsed-field gel electrophoresis, since ribotyping was not able to distinguish all strains tested. The results obtained revealed that the outbreak was caused by at least two strains: one presenting phage type 4-4a and pulsed-field patterns A1 or A2 and L+ or L-, and another presenting phage type 2 and pulsed-field patterns A1 or A2 and L+ or L-. The results indicate that the outbreak was more extensive than initially thought and that the Virchow serotype is very clonal in Spain.