Epidemiologic features of Kawasaki disease distinguished by seasonal variation: an age-specific analysis.

PURPOSE: The purpose of this study was to review the seasonal variation of Kawasaki disease (KD) by an age-specific analysis to clarify the distribution of infectious agents. METHODS: Data obtained from nationwide surveys of KD in Japan, which targeted patients for 12 years (2003-2014), were analyzed. The monthly numbers of patients were classified into the following age groups: 0-11 months, 1 year, 2-3 years 5 months, and 3 years 6 months-4 years. Factors associated with disease onset were analyzed using a 12-month moving average method. RESULTS: In winter, a sharp peak was observed in all age groups, but this was notably sharper in the 1-year age group. Plateaus in disease occurrence were observed in two periods: from March to May in the 2- to 4-year age group and from June to August in the 0- to 11-month age group. Seasonal index was analyzed into two factors that differed depending on the age group. CONCLUSIONS: The age-specific analysis of KD clearly identified age-related differences in the seasonal occurrence of this disease.

Sequential transition of the injury phenotype, temperature-dependent survival and transcriptional response in Listeria monocytogenes following lethal H2O2 exposure.

The food-borne pathogen Listeria monocytogenes is present persistently in food processing environments, where this bacterium is exposed to various stress factors, including oxidative stress. This study aimed to elucidate the temperature-dependent response of L. monocytogenes to H2O2 exposure and the phenotypic changes in colony formation by H2O2-treated bacteria. Survival curves indicated an increase in the resistance to H2O2 in L. monocytogenes as the temperature decreased during the stress exposure procedure. Transcriptional induction of genes with key roles in response to H2O2, including sigB and kat, was observed at 37°C, but not at 20°C, whereas other stress response genes were induced at both temperatures. Following H2O2 exposure, L. monocytogenes produced small colony phenotypes and the colony size decreased in a stress exposure duration-dependent manner. Resuscitated cells with no ability to form colonies in the absence of sodium pyruvate were also found. Our findings show the possibility that a sequential transition in the injury phenotype from small colony phenotype to resuscitated cells occurred during the course of exposure to H2O2. The higher H2O2 resistance at 20°C than 37°C suggests further investigation of the response to H2O2 exposure under the lower temperatures, including refrigeration temperature, which may contribute to elucidation of bacterial survival over extended time periods in food-processing environments.

Epidemiologic features of Kawasaki disease: Winter versus summer.

BACKGROUND: The epidemiology of Kawasaki disease (KD) shows seasonal variations, although the etiology of KD is unknown. In this study, we compared the clinical epidemiology of KD onset in winter versus that in summer to identify its etiology, that is, infectious agents. METHODS: Epidemiologic features of KD were compared between two seasons with high incidence (January [winter] and July [summer]) using a dataset of the 22nd nationwide survey in Japan. Data on patients who visited hospital during 2011-2012 in Japan were analyzed after adjusting for age differences. Subgroup analysis was carried out for day of illness at the day of first hospital visit. RESULTS: The total number of KD patients reported in the survey was 26 691. The number of patients who visited hospital with KD for the first time in January and July was 2,812 and 2,302, respectively. The proportion of patients in the age group 15 months-3 years was 38.8% in January and 33.5% in July. Mean serum albumin was significantly lower in January than in July (at days 2-5 of illness, P < 0.05). There were no between-group differences with respect to treatment, incidence of cardiac lesions, recurrence, or history of KD among the patients' siblings and parents. CONCLUSION: No significant differences were observed between KD with onset in January and July, although minor differences with respect to age distribution and serum albumin were observed.

Genetic classification of Listeria monocytogenes serotype 4b strains, including epidemic clones, isolated from retail meat in the Tokyo metropolitan area.

A food-borne pathogen, Listeria monocytogenes serotype 4b, has been frequently isolated from patients with listeriosis, and numerous outbreaks of listeriosis are associated with this serotype. In the present study, we performed subtyping of L. monocytogenes serotype 4b strains on the basis of genetic analyses. Thirty-four isolates of serotype 4b were classified into 8 genotypes, namely genotypes 12, 15, 16, 17, 18, 23, 24, and 25, on the basis of the sequence for the partial iap gene. Genetic analyses revealed that genotype 16 and genotypes 24 and 25 belong to epidemic clone I (ECI) and ECII, respectively, which have been frequently associated with listeriosis outbreaks in the United States and Europe. The genotype isolated most frequently from retail meats in the Tokyo metropolitan area was genotype 12 (52%), followed by genotype 16 (29%), which belongs to ECI. We suggest that ECI is a common subtype of L. monocytogenes in retail meat in the area under investigation. On the other hand, ECII isolates were confirmed to be present in retail meat in Japan but were rare.

Biofilm formation under different temperature conditions by a single genotype of persistent Listeria monocytogenes strains.

Some Listeria monocytogenes strains, termed persistent strains, originate from the same processing plant and have the ability to survive and grow over extended periods of time at contamination sources. In order to evaluate biofilm formation by such persistent strains, we isolated the pathogen from chicken samples collected from the same retail shop in repeated visits over 6 months. Strains that were of serotype 1/2b and were assigned to the same genotype by multi-virulence-locus sequence typing analysis were isolated on repeated occasions from December 1997 to June 1998 and thus were defined as persistent strains. In the present study, biofilm formation by the persistent strains was evaluated using microplates at 30 and 37°C. The biofilm-forming capability was measured after cells attaching to the microplate well were stained with crystal violet. Comparison of biofilm formation at 30°C among the persistent strains showed that a significantly higher amount of the stain was obtained from the persistent strains isolated from December to March than from those isolated from April to June. However, no significant difference in biofilm formation at 30°C was observed between persistent and nonpersistent groups of L. monocytogenes strains. In contrast, biofilm formation at 37°C was consistent among the persistent strains, and they produced significantly more biofilm at 37°C than did the nonpersistent strains. The persistent strains were also found to change their biofilm-forming ability in a temperature-dependent manner, which may suggest that the persistent strains alter their biofilm formation in response to changing environmental factors.

Seasonal patterns of legionellosis in Saitama, 2005-2009.

Sporadic cases of legionellosis have increased in Saitama Prefecture. This study aimed to understand the characteristics and incidence of legionellosis in Saitama Prefecture by studying the corresponding data from Tokyo and all over Japan. We analyzed cases of legionellosis registered from 2005 through 2009 in the annual reports of the Infectious Disease Surveillance Center. There were two peaks in the incidence of legionellosis in Japan between June and November, and a trough between February and May every year. Similar seasonal characteristics were observed in both Tokyo and Saitama. Proper management of risk factors-such as cooling towers and other aerosol-generating devices, before and during the seasonal increase in these incidences-is essential as a prophylactic measure against legionellosis.

Prevalence of Listeria monocytogenes in retailed meat in the Tokyo metropolitan area.

This study was conducted to determine the prevalence of Listeria monocytogenes in retailed meats, comprising beef, chicken, and pork, in the Tokyo metropolitan area. A total of 379 samples of retailed meat were collected from 1998 to 2003, most of which were obtained by simultaneously purchasing the three classes of meat from a shop and then making another simultaneous purchase of meat from the same shop a few weeks later. The prevalence of L. monocytogenes was 28.0%, and the serotypes isolated were mainly 1/2a, 1/2b, 1/2c, and 4b. Comparison of the prevalence of each serotype among the classes of meat showed a predominant distribution of serotypes 1/2a, 1/2b, and 4b in chicken, while serotype 1/2c was dominant in pork. A total of nine cases considered to be due to persistence and/or cross-contamination were found. Most of the strains involved in persistence and/or cross-contamination were of serotypes 1/2c or 4b. These results suggest that contamination in retailed meat in Japan is at almost the same level as in other countries and that chicken has the highest potential as a source of contamination and infection. In addition, we suggest that the ecological niche of serotype 1/2c is distinct from those of 1/2a, 1/2b, and 4b, which may explain why human hosts have less opportunity to be exposed to serotype 1/2c and why there is a lower rate of isolation of this serotype from cases of human listeriosis.

Invasion assay of Listeria monocytogenes using Vero and Caco-2 cells.

The invasion ability of Listeria monocytogenes into cultured cells has been used to evaluate its pathogenicity. In this study, invasive ability was investigated using Vero and Caco-2 cell lines. The form of invasion showed no morphological differences between both cell lines inoculated with L. monocytogenes L89-H2 or L96-23C1 strains when double fluorescence stained with rhodamine and FITC or with Giemsa staining. Recovery count and recovery rate of L. monocytogenes from Vero cells was related to the number of inoculated bacteria (2 x 10(5) to 2 x 10(7)/ml) in a bell-shape pattern, though the relationship was unclear in Caco-2 cells. Recovery rate of L. monocytogenes was higher in Vero cells than Caco-2 cells at a multiplicity of infection (MOI) 10, though the rates in both cells showed different stable stages over a considerably wide range of MOI. The recovery rate of all five L. monocytogenes strains from listeriosis patients was 15% at MOI 10 from infected Vero cells, while meat-derived strains showed variable rates regardless of the serovar. These results suggest that the Vero cell line is suitable for an invasion assay and that a recovery rate of 15% may be the critical limit for the expression of pathogenicity in the host.

Comparison of genomic structures in the serovar 1/2a Listeria monocytogenes isolated from meats and listeriosis patients in Japan.

Foodborne disease by Listeria monocytogenes, serovar 1/2a has recently been reported in many countries. Although contamination by this bacteria is also known to be gradually spreading among the marketed foods of Japan, there is little information on relation between listeriosis and food contamination. In the present study, the characteristics of the genomic structures of serovar 1/2a were compared among the isolates from marketed meats and listeriosis patients. Several isolates from meats purchased at the same shop on different days had the same genomic structure, and prolonged contamination was suggested by the conditions in the shop. Genomic structures of one strain isolated from meat were identical to those of two isolates from a patient. Another isolate was obtained from meats purchased at two different shops, and this isolate was also identical to that of the isolates from another patient. These findings suggest that the isolates from meat may have caused the listeriosis in the patients, and that the strains may have somehow traveled between the shops.

Discrimination of Listeria monocytogenes contaminated commercial Japanese meats.

Discrimination was attempted on 14 Listeria monocytogenes strains isolated from commercially available Japanese pork and chicken. Examination of the isolates was performed by restriction fragment length polymorphism (RFLP) analysis of the chromosomal DNA and amplified products and comparison of the nucleotide sequences of the amplified products. A polymorphism region containing the repeated sequences in the iap gene was amplified by the polymerase chain reaction (PCR). The genetic analyses could discriminate the 14 isolates in combination with traditional serotyping, and some strains isolated from different meats were confirmed to have a genetically close relationship. Genetic analyses used in the present study would be useful for the elucidation of the pathogen tracks from contaminated sources to humans and of the ecological niche in the food environment.