Changing epidemiology of human salmonellosis in Hong Kong, 1982-93

Nontyphoidal Salmonella infection in children: relation to bacteremia, age, and infecting serotype

BACKGROUND

Salmonella gastroenteritis, usually self- limited, can result in bacteremia and focal disease. This study was undertaken to determine the role of age and infecting Salmonella serotype on the risk of bacteremia in children.

METHODS

This was a review of medical records of children with positive nontyphoidal Salmonella cultures seen in an urban setting at the Children's Hospital of Michigan in Detroit between July 1993 and December 2007.

RESULTS

Isolates recovered from 633 patients, representing 50 serotypes, included 594 positive stool cultures and 72 (11.4% of all patients) positive blood cultures. Salmonella serotype Typhimurium was the most common serotype, accounting for 29.4% (186/633) of isolates, of which only 3 (1.6%) were recovered from blood. The most common serotype recovered from blood was serotype Heidelberg (40/120 of patients with Heidelberg serotype) accounting for 55.5% (40/72) of positive blood cultures. The patients' age range was 2 weeks to 20 years, with a median of 7 months (interquartile range, IQR = 4-23 months). Bacteremic patients (n = 72) had a median age of 6.5 months (IQR = 4-11 months) and were comparable in age to non-bacteremic patients (n = 266), who had a median age of 5.5 months (IQR = 3-11 months) (p = 0.24). The odds ratio (OR) for bacteremia in patients infected with serotype Typhimurium was 0.21 and in patients with serotype Heidelberg was 4.0. Patients with serotype Heidelberg infection in the age groups < 3 months, 3-6 months, 6-12 months, and > 12 months had an OR for bacteremia of 9.2, 2.5, 3.2, and 6.0, respectively.

CONCLUSION

In our patient population, children with Salmonella serotype Heidelberg infection are at higher risk of bacteremia than children infected with other Salmonella serotypes. The risk is highest during the first 3 months of life.

Typhoid fever in children in Africa

Estimates for the year 2000 suggested that there were approximately 21.5 million infections and 200,000 deaths from typhoid fever globally each year, making the disease one of the most serious infectious disease threats to public health on a global scale. However, these estimates were based on little data, especially from Africa. Global prominence and high-profile outbreaks have created the perception in Kenya that typhoid is a common cause of febrile illness. The Widal test is used widely in diagnosis. We have reviewed recent literature, taking the perspective of a healthcare provider, to collate information on the prevalence of typhoid in children particularly, and to explore the role of clinical diagnosis and diagnosis based on a crude, but common, interpretation of the Widal test. Data suggest that typhoid in children in rural Africa is uncommon, perhaps 100 times or 250 times less common than invasive disease because of Haemophilus influenzae or Streptococcus pneumoniae, respectively. Frequent use of the Widal test may result in many hundreds of over-treatment episodes for every true case treated and may perpetuate the perception that typhoid is common. Countries such as Kenya need better bacterial disease surveillance systems allied to better information for healthcare providers to promote appropriate decision-making on prevention and treatment strategies.

Salmonella serovars isolated from humans in São Paulo State, Brazil, 1996-2003

Salmonellosis remains an important cause of diarrheal illness in humans in São Paulo State, Brazil. In this study were identified 3554 Salmonella isolates from human infections, during the period 1996-2003. Among 68 different serovars determined, S. Enteritidis was the most frequent one in gastrointestinal and extra-intestinal infections accounting for 67.4% of all isolates. S. Typhimurium and S. enterica subsp. enterica (4,5,12:i:-) were most frequently isolated from children aged < 1-4 year-old, in contrast, people with S. Enteritidis infections were most likely to be 20-50 year-old. In our geographic area the continued laboratorial surveillance of salmonellosis, including serotyping, has showed the trends in Salmonella serovars causing infections in humans throughout the time.

Association of Laribacter hongkongensis in community-acquired gastroenteritis with travel and eating fish: a multicentre case-control study

BACKGROUND

Laribacter hongkongensis has been recovered from several patients with gastroenteritis. However, the causative role of this organism in human gastroenteritis is still unproven, and sources of the bacterium are unknown. We undertook a multicentre case-control study to investigate the association of L hongkongensis with gastroenteritis.

METHODS

Faecal samples from patients with community-acquired gastroenteritis and controls were cultured for L hongkongensis. Targeted food surveillance was done to identify potential sources of this bacterium. All isolates of this organism from patients and food items were characterised by pulsed-field gel electrophoresis and ribotyping.

FINDINGS

During a 4-month period, L hongkongensis was recovered from 17 of 3788 patients with community-acquired gastroenteritis, but was absent in 1894 controls (p=0.001). Those who were culture-positive for this bacterium had a recent history of travel (ten [59%] patients vs two [6%] of 34 matched controls, p<0.0001), of fish consumption (16 [94%] vs 19 [56%], p=0.009), and of eating minced freshwater fish meat (five [29%] vs one [3%], p=0.012). We recovered 25 L hongkongensis isolates from intestinal samples of freshwater fish and two from minced freshwater fish meat. Bacteria with the same pulsed-field gel electrophoretic pattern and ribotype were recovered from one patient and a sample of minced freshwater fish meat, which was from the same retail market recently visited by the patient. We did not see this particular combination of electrophoretic pattern and ribotype in any other isolates.

INTERPRETATION

L hongkongensis is associated with community-acquired gastroenteritis and traveller's diarrhoea. However, its causative role has not been shown. Freshwater fish is one source of this bacterium.

Serotypes, virulence factors, antibiotic sensitivity, beta-lactamase activity and plasmid analysis of Salmonella from children with diarrhea in Tripoli (Libya)

A total of 21 Salmonella strains isolated in Libya (16 from children with diarrhea and 5 from healthy controls) were serotyped and studied for their cell invasive ability, production of cytotoxin, antibiotic susceptibility, beta-lactamase activity and plasmid profiles. Eight different serotypes of Salmonella were identified: 6 S. saintpaul, 4 S. wien (1 from control), 2 S. newport, 2 S. muenchen (1 from control), 2 S. typhimurium (1 from control), 2 S. hadar (1 from control), 2 S. reading (1 from control), 1 S. kottbus. Twenty (95%) were positive in the invasiveness assay using HeLa cells, and all (100%) were negative for cytotoxin production in HT29 cells. More than 40% were resistant to ampicillin, cefalexin, cefamandole, cefoperazone, chloramphenicol, gentamicin, mezlocillin and trimethoprimsulphamethoxazole and 100% were susceptible to the new quinolones. Most (67%) of the strains harbored plasmids and 43% produced beta-lactamase. A strong association was observed between the presence of more than one plasmid, beta-lactamase activity, and multiple-resistance to antimicrobial agents and serotypes S. saintpaul and S. wien. Curing experiments with acridine orange showed that 2 plasmids (33 and 1.4 megadaltons) might be responsible for the resistance to chloramphenicol and gentamicin. The present study demonstrated that multiple-resistant salmonellae are widespread in Libya and the resistance is mainly plasmid mediated.

Clinical and prognostic categorization of extraintestinal nontyphoidal Salmonella infections in infants and children

The study included 172 patients, aged 0-15 years, for whom at least 1 nonfecal, nonurinary specimen was culture-positive for nontyphoidal Salmonella. Ninety-five percent had positive blood cultures. Immunocompromising diseases were found in 19% of 74 infants and 77% of 98 children. Associations between the study factors and outcomes, as localized infection or death, were assessed by logistic regression analysis. Thirty-three patients had localized infections. An adjusted risk factor for development of localized infections was an age of <12 months (P=.003). There were 17 deaths. The case-fatality rates were 43% and 10% for immunocompromised and 5% and 0% for nonimmunocompromised infants and children, respectively. Adjusted risk factors for death were age of <12 months (P=.006), inappropriate antimicrobial therapy (P=.014), meningitis or culture-proven pneumonia due to nontyphoidal Salmonella (P=.004), and immunocompromised status (P<.001). The clinical courses and prognoses for infants and children with extraintestinal infection due to nontyphoidal Salmonella can be categorized into 4 groups according to the characteristics of age (infants vs. children) and host status (immunocompromised vs. nonimmunocompromised).

Antimicrobial susceptibilities and molecular epidemiology of Salmonella enterica serotype enteritidis strains isolated in Hong Kong from 1986 to 1996

The incidence of salmonellosis has been increasing in Hong Kong since 1989. The most common Salmonella enterica serotype isolated in 1994 was S. enteritidis. The antimicrobial susceptibilities and molecular epidemiology of 275 S. enteritidis strains isolated in this locality between 1986 and 1996 were studied. Over 99% of the isolates were susceptible to 17 of the 19 antimicrobial agents tested. One isolate harbored an autotransferring plasmid that confers resistance to tetracycline and trimethoprim-sulfamethoxazole. Another isolate harbored a mobilizable plasmid that confers resistance to ampicillin and cephalothin. This isolate was found to produce a beta-lactamase with a pI of 5.2. A total of 264 isolates (96%) were found to harbor one to five plasmids, and the majority (254) harbored a 60-kb plasmid. Of these isolates, 94% contained identical 60-kb plasmids. Based on plasmid profiles, plasmid and chromosomal fingerprints, ribotypes, and randomly amplified polymorphic DNA (RAPD) patterns, 170 (62%) isolates were allocated to group 1b. About 90% of isolates had identical or similar DNA fingerprints, ribotypes, and RAPD patterns, suggesting that a predominant clone of S. enteritidis was circulating in Hong Kong during the period being studied.

Changing patterns of Salmonella serovars: increase of Salmonella enteritidis in São Paulo, Brazil

Serovars of a total of 5,490 Salmonella strains isolated during the period of 1991-95, from human infections (2,254 strains) and from non-human materials (3,236 strains) were evaluated. In the studied period, 81 different serovars were determined among human isolates. Salmonella Enteritidis corresponded to 1.2% in 1991, 2% in 1992, 10.1% in 1993, 43.3% in 1994, and 64.9% in 1995 of all isolates. A significant rise on the isolation of this serovar was seen since 1993 linked to food poisoning outbreaks. It is reported also an increase on the isolation of S. Enteritidis from blood cultures, associated mainly with patients with immunodeficiency syndrome. S. Enteritidis was prevalent among one hundred and thirty different serovars isolated from non-human sources. Increasing number of isolation of this serovar was seen from shell eggs, breeding flocks and from environmental samples. It is also reported a contamination of commercial feed stuffs by S. Enteritidis which represents a major concern for Brazilian poultry industry.

Detection and serogroup differentiation of Salmonella spp. in food within 30 hours by enrichment-immunoassay with a T6 monoclonal antibody capture enzyme-linked immunosorbent assay

We previously described an antigen capture enzyme-linked immunosorbent assay which makes use of monoclonal antibody T6, which recognizes an epitope on the outer core polysaccharide of Salmonella lipopolysaccharide molecules that is common to almost all Salmonella serovars. In this paper, we show that this assay can detect between 10(5) and 10(7) Salmonella cells per ml even in the presence of excess Escherichia coli. A total of 153 of 154 (99%) serogroup A to E strains and 51 of 78 (71%) serogroup F to 67 strains were reactive as determined by this assay. This corresponds to a detection rate of approximately 98% of all salmonellae known to affect humans. None of the 65 strains of non-Salmonella bacteria tested positive. Taking advantage of the O-factor polysaccharides also present on the antigen captured by the immobilized T6 antibody, we showed that 136 of 154 Salmonella serogroup A to E strains (88%) were correctly differentiated according to their serogroups by use of enzyme conjugates of a panel of O-factor-specific monoclonal antibodies. We evaluated this assay for the detection and serogroup differentiation of salmonellae directly from enrichment cultures of simulated food, eggs, pork, and infant formula milk. All 26 samples which had been contaminated with Salmonella spp. were detected by T6 (100% sensitivity), with only one false-positive result from 101 samples not contaminated by Salmonella spp. (99% specificity). The detection time was substantially reduced to between 17 and 29 h, depending on the enrichment methods used. Since there were no false-negative results, we concluded that this enrichment-immunoassay method can afford rapid screening for Salmonella spp. in food samples.