Epidemiological News Bulletin

Transcription

1 PUBLICATION OF THE COMMITTEE ON EPIDEMIC DISEASES Epidemiological News Bulletin MARCH 2001 VOL. 27 NO. 3 ISSN Surveillance of multi-drug resistant Salmonella typhimurium The emergence of Salmonella strains that are resistant to commonly used antibmicrobials is important to clinicians, microbiologists and those responsible for the control of foodborne infectious diseases. Salmonella typhimurium definite type 104 (DT104) or phage type 104 (PT104) with resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide and tetracycline (ACS Su T) was first reported in the UK in Since then, it has been reported with increasing frequency in other European countries, Japan and the United States. In the UK, it is the second most prevalent type of Salmonella isolated from humans. Outbreaks related to this strain have also been reported in Ireland, Northern California and Denmark. In Singapore, laboratory surveillance to monitor the introduction of multidrug-resistant S. typhimurium strain is undertaken by the National Enteric Bacteria Centre of the Department of Pathology, Singapore General Hospital. The centre undertakes serotyping of all Salmonella isolates submitted by the clinical laboratories of hospitals. S. typhi, S. paratyphi, S. enteritidis and S. typhimurium are also phage typed. In July 2000, an unusual increase in the isolation of S. typhimurium PT104L with resistance to ampicillin, chloramphenicol, gentamicin, streptomycin, tetracycline and sulphonamide or R-type ACGSTS3), was noted. The isolates came mainly from the stool cultures of children below 18 months of age. The Quarantine & Epidemiology Department of the Ministry of the Environment was notified and epidemiological investigations were conducted. Epidemiological investigations Infants and toddlers aged between one month and 36 months whose stool cultures were positive for S. typhimurium DT104L during the period July- August 2000 were traced to determine the source of CONTENTS Surveillance of multi-drug resistant Salmonella typhimurium... P. 15 The infectious disease situation in P. 18 Epidemiological News Bulletin readership survey... P. 20 Cases of specified notifiable diseases... P. 22

2 16 infection and the mode of transmission. The home of each child was visited to look for other unreported cases among contacts. The parent, guardian, or domestic maid was interviewed by two trained environmental health officers using a structured questionnaire. Over 90 questions were included to elicit clinical and epidemiological information such as intake of different food items, food handling and personal hygiene practices in the kitchen and contact with household pets with diarrhoea. For each notified case, 2-3 controls comprising children of the same age group (within 6 months of the age of the case), gender and ethnic group living in the same neighbourhood, and with no recent travel history and gastro-intestinal symptoms during the previous 2 weeks, were selected and interviewed. The questionnaire covered 3 days preceding the onset of symptoms of the cases, and for the controls, 3 days preceding the interview. Samples of milk powder, cereal and other food items were obtained from the homes of the cases and retail outlets, and submitted to the Food and Water Laboratory, Singapore General Hospital, for isolation of Salmonella species. Differences in proportion between cases and controls were examined using chi-square or Fischer s exact test; a p-value of <0.05 was considered to be statistically significant. Results During the period 13 July 17 October 2000, a total of 33 isolates of S. typhimurium of the same R-type ACGSTS3 and of the same phage type 104L were identified. Their PFGE patterns were indistinguishable. Of the isolates, 17 were detected in July, 10 in August, 4 in September and 2 in October. Except for 4 adults aged between 31 years and 66 years, all the others were toddlers and infants as young as 2 days of age. There were 19 males and 14 females (Table 1). None of them had a recent travel history outside Singapore. All the cases occurred singly and sporadically and were not clustered in any particular locality. No secondary cases were identified in the same household. The main presenting clinical symptoms of 19 cases investigated were watery diarrhoea (100%), fever (78.9%), vomiting (52.6%) and abdominal cramps (26.3%). About 58% had bloody stool. Seventeen of them were hospitalised and 2 were treated as outpatients. No death was reported. Results of the case-control study based on 19 cases and 55 controls implicated porridge with ikan bilis (dried anchovy) as the vehicle of transmission (p<0.01). No other food items or risk factors were incriminated (Table 2). Table 1 Age-gender distribution of 33 reported cases of S. typhimurium phage type 104L, Singapore Age group Male Female Total <6 months months 11 months year years years years years years years years years TOTAL

3 17 None of the food samples taken from the homes of 6 cases, including one sample of grounded dried anchovy, were positive for Salmonella species. Salmonella group E was isolated from one of the 16 samples of dried anchovies subsequently purchased from the retail outlets. However, further samples collected were repeatedly free from Salmonella contamination. Comments Periodic outbreaks of salmonellosis caused by multidrug resistant strains occurred periodically in Singapore: S. typhimurium in , S. orainberg in , and S. blockley in However, the vehicle of transmission could not be determined. The predominant serotypes in 1999 were Table 2 Results of matched case-control analysis in an outbreak of Salmonella typhimurium PT104L, Jul to Oct 2000 Egg Food items/risk factors Cases (n=19) Controls (n=55) OR 95%CI p-value Uncooked 0/19 1/ Partially cooked 4/19 12/ Cooked 3/19 23/ Dairy products Powdered milk formula 18/19 48/ Pasteurised milk 1/19 6/ Reconstituted/UHT milk 0/19 1/ Cereals with milk 8/19 21/ Baby food 1/19 1/ Cheese 9/19 13/ Yoghurt 0/19 4/ Yakult 2/19 12/ Vitagen 2/19 9/ Porridge Alone 6/19 10/ With chicken 4/19 26/ With pork 7/19 29/ With beef 0/19 4/ With liver 1/19 6/ With ikan billis (dried anchovy) 14/19 14/ Breast fed With supplements 0/19 1/ Without supplements 0/19 4/ Fruits 11/19 21/ Fruit juices 4/19 11/ Raw vegetables 0/19 2/ Animal contact 0/19 3/ Household contact with diarrhoea 0/19 5/ Handwashing before preparing food 13/19 51/ Storage of ikan bilis in chiller 4/19 10/

4 18 S. enteritidis (20.3%), S. stanley (12.8%) and S. weltevreden (10.8%), followed by S. typhimurium (7.3%). The risk factors for S. typhimurium DT104 infection in developed countries include contact with ill farm animals and consumption of chicken, pork sausage and meat paste. Consumption of contaminated beef, turkey and raw-milk cheese has also been implicated in outbreaks. This outbreak of S. typhimurium DT104L was associated with the consumption of grounded ikan bilis (dried anchovies). However, the same strain was not detected from samples taken from the retail outlets, although another serogroup (Salmonella group E) was detected. Salmonella is one of the most prevalent enteric pathogens encountered in seafood. It has been isolated from ready-to-eat imported seafood such as cooked shrimp, shellfish, fish paste, smoked fish, salted dried fish and caviar in the US. Outbreaks of salmonellosis caused by ingestion of contaminated cuttlefish chips snack have been reported in Japan. In Singapore, the ikan bilis was imported from Thailand, Vietnam, Malaysia and Indonesia and sold at retail outlets throughout the country. The small anchovies caught in fishing villages in these countries were lightly salted and dried outdoor. This method of processing ikan bilis is subject to gross environmental contamination, including excreta of birds, rats and flies. After processing, the dried seafood was packed in gunny sacks and exported. It was transported by container trucks, fishing boats or lorries to Singapore. Further contamination could have occurred during transport, storage and display at retail outlets where it was usually sold without proper packing and labelling. The dried anchovy is a rich source of calcium and protein and is a popular ingredient for the preparation of a variety of foods, including soup stock. It is commonly deep fried and served with chilli. If used as an infant feed, the common practice is to ground it and then cooked with porridge. In this outbreak, it was found that in the households where cases had occurred, the ikan bilis was first grounded and stored in a container at room temperature for subsequent use. It was either sprinkled onto or added to freshly cooked porridge, instead of boiling with the porridge, and served. This is an isolated incident believed to be due to a batch of contaminated ikan bilis imported into the country. The dried anchovy should be thoroughly cooked before consumption. The practice of sprinkling or adding grounded ikan bilis onto cooked porridge should be discouraged as the temperature attained would not be adequate to destroy the Salmonella present in the food. The infectious disease situation in 2000 The infectious disease situation in Singapore was closely monitored through a well-established system of epidemiological surveillance. A high level of vigilance on the disease activity was also maintained on emerging infectious diseases throughout the world to prevent their introduction into

5 19 Singapore and to deal with them swiftly and effectively should they be detected. On 1 October 2000, three infectious diseases were made legally notifiable, viz. hand, foot and mouth disease, legionellosis and Nipah virus infection. The trend of vector-borne, food-borne and vaccine-preventable diseases is shown in Fig. 1. Vector-borne diseases There was a marked decrease in the incidence of dengue fever (DF)/dengue haemorrhagic fever (DHF) from 1,355 cases in 1999 to 673 cases in One death (imported case) was reported. Most of the cases occurred in the south-eastern and north-eastern parts of the island. A total of 266 cases of malaria were reported. Majority (99%) of the cases were imported, mainly from the Indian subcontinent and Southeast Asia. No case of Japanese encephalitis was reported. Food-borne diseases The incidence of cholera remained low with 7 indigenous and 3 imported cases reported. The incidence of indigenous typhoid and paratyphoid was also low with 14 and 2 cases reported, respectively. Majority of the notified cases of typhoid (82.5%) and paratyphoid (90.5%) were imported. There were 13 indigenous cases of hepatitis A and 3 indigenous cases of hepatitis E cases. 64 (83.1%) of 77 reported cases of hepatitis A and 14 (82.4%) of 17 cases of hepatitis E were classified as imported. A total of 213 notifications of food poisoning involving 1,542 cases were reported. A water-borne outbreak of 122 cases occurred in a shopping, office and residential complex at Bukit Timah. The incidence of Campylobacter enteritis decreased from 344 cases in 1999 to 231 cases in The incidence rate was highest in children below the age of five years. Air-borne diseases There were 509,966 attendances at government outpatient clinics for acute respiratory illnesses and 26,077 attendances for conjunctivitis. The incidence of chickenpox decreased from 31,592 cases in 1999 to 24,074 cases in Mumps also declined from 6,384 cases in 1999 to 5,981 cases in 2000 and rubella from 432 cases in 1999 to 312 cases in However, the incidence of measles increased from 65 cases in 1999 to 141 cases in No local cases of diphtheria or pertussis were reported. Environment-related diseases A total of 55 cases of legionellosis and 67 cases of melioidosis were reported. Those at higher risk were males over 55 years of age. Hand, foot and mouth disease A cluster of four deaths clinically related to hand, foot and mouth disease occurred in Aug and Sep. Closure of all preschool centres effectively brought the outbreak under control.

6 20 Rate per 100,000 population Figure 1 Annual incidence rates of specified vector-borne, food-borne and vaccinepreventable diseases in Singapore, Vector-borne diseases Dengue fever/dengue haemorrhagic fever Japanese encephalitis+ Malaria Rate per 100,000 population Food-borne diseases Cholera Typhoid fever Paratyphoid fever Hepatitis A Rate per 100,000 population Vaccine-preventable diseases Diphtheria* Poliomyelitis* Measles Hepatitis B Ye ar * No local cases of diphtheria and poliomyelitis were reported during this period + One imported case of Japanese encephalitis were reported in 1996, two imported cases in 1997, one imported case in 1998 and one imported case in 1999 MIX002/CMH/ Epidemiological News Bulletin readership survey In May 2000, the Quarantine & Epidemiology Department of the Ministry of the Environment conducted an Epidemiological News Bulletin Readership Survey. The intent of the survey was to obtain feedback from the readers in order to improve the relevance and quality of the information in the monthly bulletin. A total of 116 (3.4%) out of 3390 readers in the mailing list responded. These included private general practitioners, government and private hospital physicians and health administrators. Readers from countries such as the USA and China also participated. The results are as follows: a) How do you usually obtain the Epidemiological News Bulletin? Personal copy : 91.4% Department copy : 8.6% Website : 0% Colleagues s copy : 0% Others : 0% b) How long do you usually take to read it? Less than half an hour : 86% More than half an hour :14%

7 21 c) Do you circulate it to other members of your staff? Yes : 45.9% No : 54.1% d) Which of the following categories of health service do you belong to? General practice : 61.2% Private hospital : 14.7% Govt/restructured hospital : 6.0% University : 3.5% Health administration : 2.5% Armed forces medical service : 0.9% Govt primary health service : 0% Others : 11.2% e) Do you find the bulletin useful in your work? Yes : 98.2% No : 1.8% f) How would you grade the usefulness of the following regular features? i) Surveillance of specific infectious diseases (scale of 0-5) 5 (most useful) : 54.8% 4: 32.2% 3: 12.2% 2: 0% 1 (least useful) : 0% 0 (not useful) : 0.9% ii) Monthly statistics of notifiable diseases (scale of 0-5) 5 (most useful) : 27.8% 4: 25.2% 3: 32.2% 2: 9.6% 1 (least useful) : 4.3% 0 (not useful) : 0.9% g) Topics which the respondents would like to be in cluded: Regional statistics, epidemic news and trends Antibiotic resistance update Treatment options/modalities available for diseases AIDS/STD/non-communicable disease update Advice on vaccination/prophylaxis Identification and management of outbreaks Information sheets on common conditions for patients on the move h) General remarks: Extremely useful in providing local perspective on infectious disease. Good supplement to textbook. Essential reading for all doctors, medical students and nurses in Singapore Very good work. Keep it up. Keep sending. I find the bulletin useful and look forward to monthly issues. Excellent review - I always read it and refer to back copies frequently Like its small format while others preferred A4 format, easier for filing would be more convenient make available on interactive website Requests for color photographs and more charts Request for case studies and reports

8 Cases of specified notifiable diseases, Republic of Singapore, February 2001 Month ending Cumulative, first 9 weeks Disease s Median Median 3 Mar 01 4 Mar Cholera Plague Yellow fever Chickenpox Dengue a) Dengue fever b) Dengue haemorrhagic fever Diphtheria Enteric fevers a) Typhoid fever b) Paratyphoid fever Leprosy Malaria Poliomyelitis Venereal diseases a) Chancroid b) Gonorrhoea c) Non-specific urethritis d) Syphilis i) Infectiou s ii) Non-infectious AIDS Tuberculosis Viral hepatitis a) Hepatitis A b) Hepatitis B c) Others Viral encephalitis Measles Mumps Rubella Hand, foot and mouth disease Legionellosis Nipah virus infection The data in this Bulletin are provisional, based on reports to the Quarantine & Epidemiology Department, Ministry of the Environment, and the Department of Clinical Epidemiology, Tan Tock Seng Hospital. Any comments or questions should be addressed to: The Editor Epidemiological News Bulletin Quarantine & Epidemiology Department Environment Building, 40 Scotts Road, Singapore Editorial Board Editor : A/Prof Goh Kee Tai - Head, Quarantine & Epidemiology Department, Ministry of the Environment Scientific Advisory Committee : Prof Tan Chorh Chuan - Director of Medical Services, Ministry of Health Prof Chan Soh Ha - Head, Department of Microbiology, National University of Singapore Dr Sng Ewe Hui - Emeritus Consultant, Department of Pathology, Singapore General Hospital