Acute Gastrointestinal Illnesses cost five million work days

A major New Zealand Food Safety Authority (NZFSA) study, conducted for NZFSA by ESR, estimates that more than five million working days are lost each year in New Zealand due to gastrointestinal illness. It also concludes that data from the notifiable disease reporting system may not be the most efficient way of providing risk management information for widespread illnesses such as diarrhoea and vomiting.

"The Acute Gastrointestinal Illness (AGI) study is a key part of the work NZFSA is doing to get an idea of the size of the problem of foodborne disease," says Dr Donald Campbell, NZFSA Principal Adviser (Public Health). "The year-long study helps us find where and how much self-reported AGI there is in New Zealand and what impact it has on those becoming ill. In addition, we were able to discover how many cases go unreported and why that might be."

The study, which indicates that New Zealand's rate of AGI of 7.8% is similar to other developed countries that have carried out similar studies, involved three parts, covering the community, GPs and medical laboratories.

"This is the first of its type in New Zealand. Previously we have had to rely on estimates. The problem is obvious – few people who get diarrhoea or vomiting go to the doctor and, of those that do, the cause of infection is not always identified because many gastrointestinal illnesses take days or even weeks to cause symptoms.

"This means that there is a 'pyramid of reporting'. This study found 219 AGI cases among the 3457 people surveyed. Of those, just 38 (22%) visited a GP with 19 stool samples requested (9%) and 17 (8%) submitted. Of these, three (2%) tested positive and only one was reported to the notification system."

Dr Campbell says that it is important to get an accurate estimate of causes of AGI in New Zealand so that health protection resources, including food safety and promotion, can be targeted to areas that will best reduce levels of these illnesses.

"The more accurate the data we have, the better we can develop ways of combating foodborne gastrointestinal illness. We need to know not only how much there is, but also where it comes from. It's like an iceberg – if the information that is being recorded is just a small fraction of the real situation we must find ways to estimate the true size of the problem. The alternative is to seek better ways of collecting more data. This study will be invaluable in both regards – it's given us a better idea of how much AGI there really is and which groups of the population are getting sick, and given us indications of possible alternatives or additions to current data collection systems."

Dr Campbell notes that there is further research to be done. "While we now have a better idea of the extent of this problem in New Zealand, we still need certainty around the causes. We need improved estimates of the proportion of illness that is foodborne as opposed to person-to-person, contracted through unsafe water, animal contact and so on. Research will continue to improve the picture."

Among the key findings of the study were:
- over the 12 month study period, the total estimated days of paid work lost due to AGI (both the sufferers and their carers) was about 5.2 million
- there are an estimated 6.5 million cases of vomiting and diarrhoea, and 4.6 million cases of Acute Gastrointestinal Illness in New Zealand every year
- cases were lowest in winter with 6.2% of people suffering AGI on any day, higher in spring (7.3%) and peaking in summer at one in every 10 (10.3%)
- although statistically not significant, more males than females (9.2 v 8.2%) reported an AGI (it is interesting that a recent Foodsafe Partnership survey on hand washing showed that women were significantly better than men at this simple infection control measure)
- as expected, children under five have a higher incidence of AGI than other age groups
- AGI prevalence is higher in Maori (11.0%) than non-Maori (8.0%)
- household size and income did not affect prevalence
- half of the people with AGI recovered by day two and 80% by day four
- 90% of people with AGI missed work or other activities, many for more than two days
- the criteria for severe AGI were met by 28% of the cases reported
- a third of people sought medical advice, with 22% getting advice from a GP (about 1.8 million cases a year seeking medical advice, and 1.0 million getting advice from a GP)
- about two-thirds of patients were either 'good' or ' very good' in complying for requests for faecal samples.
- the estimate that 0.5% of New Zealand cases of AGI are notified to national surveillance is slightly higher than estimates for Australia and Canada, but lower than for England.

The research reports are available on the NZFSA website at: http://www.nzfsa.govt.nz/science/research-projects/index.htm  

ENDS