Epidemiology of foodborne and emerging infectious diseases in Australia, 2014 to 2015

Foodborne outbreaks caused by bacterial toxins such as Clostridium perfringens, Staphylococcus aureus and Bacillus cereus are an often overlooked cause of morbidity. This study aimed to describe the epidemiology of bacterial toxin mediated foodborne outbreaks in Australia between 2001 and 2013, and to identify high risk groups and risk factors to inform prevention measures. All foodborne and suspected foodborne outbreaks in Australia are collated in the OzFoodNet Outbreak Register. Data on all confirmed or suspected bacterial toxin mediated foodborne outbreaks notified to the register and investigated between 2001 and 2013 inclusive were included. Descriptive analyses were undertaken using StataSE 13. There were 272 confirmed or suspected toxin mediated outbreaks reported, of which 107 (39%) were laboratory confirmed. These outbreaks affected 4066 people, including 70 hospitalisations and 13 deaths, 12 of which occurred in aged care facility residents. Clostridium perfringens was suspected or confirmed as the causative agent in 171 (63%) outbreaks. Commercial food service businesses (145 outbreaks, 53%) and aged care facilities (99 outbreaks, 36%) were the most commonly reported settings for outbreaks. Only seven outbreaks (3%) were associated with food prepared in private residences. Inadequate temperature control of pre-cooked foods was reported as a contributing factor in all confirmed and suspected toxin mediated outbreaks where this information was available. Bacterial toxin mediated foodborne outbreaks cause significant preventable morbidity in Australia, and disproportionately affect residents of aged care facilities, a particularly vulnerable population. Public health efforts aimed at improving storage and handling 19 practices for pre-cooked and re-heated foods could help to reduce the magnitude of this problem. Introduction While many studies have examined the epidemiology of outbreaks of pathogens such as Salmonella, few have focused on bacterial toxin mediated outbreaks (1). Some detailed analyses have included the bacterial toxin producers in larger studies of all causes of gastroenteritis (3), although in these cases, due to the focus on more common causes of gastroenteritis, such as Salmonella and norovirus, the description of the epidemiology of the bacterial toxin mediated outbreaks can be less visible. All infectious causes of gastroenteritis are underestimated in Australia as confirmation requires at least some of those affected to submit a faecal specimen for testing. The multiplication factor to account for underestimation depends on numerous factors including severity of illness and ease of testing (4-6). Outbreaks caused by toxin producing bacteria are often less severe and have a shorter duration than those caused by other pathogens making sufferers even less likely to be tested (1). Testing for bacterial toxin producing bacteria is difficult in both food and faecal samples, and is only performed at a few laboratories in Australia (John Bates, personal communication). A recent study estimating underreporting of gastroenteritis in Australia estimated the multiplier for each of the three bacterial toxin mediated illness to be 104 (5). Bacterial toxin mediated gastroenteritis can be caused by two different modes of action. The preformed toxin is, as its name suggests, formed by the bacteria in the food prior to consumption. Because the toxin has already been formed, onset of illness is rapid and can be as little as 30 minutes. Vomiting is commonly associated with intoxication caused by preformed toxin (7). Growth of the bacteria and the production of toxin occurs before the cooking kill step, and the toxin itself is heat resistant (7, 8) meaning further heating will not render the food safe to eat. Staphylococcus aureus and Bacillus cereus can produce preformed toxins (9, 10). Foodborne disease caused by a pre-formed B. cereus toxin is known as “emetic B. cereus” due to the predominant symptoms of nausea and vomiting. In contrast, the in vivo toxin is formed after consumption of contaminated food. The incubation period of this form of intoxication is longer than that for preformed toxins, but shorter than many other types of foodborne illness (which are in the order of several days), and ranges from six to 16 hours (11, 12). Clostridium perfringens and B. cereus cause this type of intoxication. Foodborne disease caused by in vivo B. cereus toxin is 20 known as “diarrhoeal B. cereus” due to the predominant symptoms of cramping and watery diarrhoea. The bacteria grow rapidly in food held at ambient temperature (10540C), and produce enterotoxin after ingestion (13). Although further cooking can kill the vegetative cells, both bacteria can produce heat-resistant spores which can then regerminate after cooking. All three toxin producing bacteria are ubiquitous in the environment, and in the case of S. aureus, is a normal component of human flora (14). A third type of foodborne toxin is the neurotoxin produced by Clostridium botulinum. This toxin is formed in the food before consumption and causes neurological illness (15). C. botulinum toxin is one of the most poisonous biological substances known and as such botulism is listed on the Australian National Notifiable Diseases List. However, few cases of C. botulinum are reported in Australia, and although a single case of botulism can be considered an “outbreak”, these single cases are reported via the National Notifiable Diseases Surveillance System (NNDSS), and are not entered into the OzFoodNet Outbreak Register and thus are not discussed further in this chapter. In Australia, infection with S. aureus, B. cereus and C. perfringens are not notifiable diseases, so cases of gastroenteritis due to these pathogens are only reported in the OzFoodNet Outbreak Register as part of an outbreak, defined as two or more cases of the same illness with a common source. OzFoodNet began entering data into the Outbreak Register in 2001. The Register is a Microsoft Access database maintained by OzFoodNet Central (located in the Australian Government Department of Health). Jurisdiction-based OzFoodNet personnel are responsible for entering the details of their outbreak investigations into their own jurisdiction-specific Access database, and are required to transmit their data to OzFoodNet Central quarterly. The Outbreak Register contains information about all outbreaks of gastroenteritis and other outbreaks that are investigated by OzFoodNet. In addition to foodborne outbreaks, this includes waterborne, animal-to-person, person-toperson and environmental outbreaks. The data collected are diverse, and include information about the illness, possible source, transmission, causes (distal, e.g. process failures and proximate, e.g. aetiology), and information about the level of evidence for these categories. Summaries of outbreaks are published in OzFoodNet quarterly and annual reports, available in the publication Communicable Diseases Intelligence.