Monthly notified cases of salmonellosis in New Zealand

New Zealand’s small population and low number of cases of some diseases mean that disease rates may vary greatly from year to year (Environmental Science and Research Limited, 2014b). The numbers of notified cases are sourced from EpiSurv, New Zealand’s national notifiable disease surveillance system. Various factors influence disease notification, and therefore the calculation of notifiable disease rates. For example, when an illness is not severe, people are less likely to consult a medical practitioner and, even if diagnosed, are less likely to be notified with laboratory confirmation.

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Bacteria and parasites like campylobacter, salmonella, and cryptosporidium can contaminate our food and water, leading to serious illness. Campylobacter, salmonella, and cryptosporidium are influenced by temperature and other climate variables, and incidence rates may increase as climate change causes temperatures to rise. Monitoring the incidence rates of illnesses can help us assess the health risks related to climate change and better prepare for disease outbreaks.

These data were sourced from nationwide doctor and laboratory notifications to public health units of campylobacteriosis, cryptosporidiosis, and salmonellosis. Notifying is when a laboratory or doctor informs a medical officer of health of a confirmed disease.
Salmonellosis and cryptosporidiosis are recommended environmental health indicators in New Zealand. They are used to monitor the effectiveness of health interventions for climate change (Hambling, 2012). The World Health Organization Regional Office for Europe (2015) identified that salmonella infection could increase with climate change. Climate-change health risks for campylobacteriosis and cryptosporidiosis have also been modelled as part of the Health Analysis and Information for Action (HAIFA) project (Environmental Science and Research Limited, 2014a). Modelling shows they are expected to increase in the future as a result of climate change. Campylobacter is a bacterium that is mainly transmitted by eating contaminated food or having contact with farm animals, including dogs and cats. Infection rates are strongly linked to temperature and tend to peak in summer. However, other factors also affect infection rates. This is shown by the significant drop in cases since late 2006, which coincides with the introduction of a range of voluntary and regulatory interventions (Sears et al, 2011).
Salmonella is a bacterium that is mainly transmitted by eating contaminated food. Warmer ambient temperatures allow the bacteria to grow faster in unrefrigerated foods, which may lead to higher rates of infection.