Water-borne diseases related to drinking-water

This factsheet presents information on how New Zealander's health is affected by three potentially waterborne diseases: campylobacteriosis, giardiasis and cryptosporidiosis.

Potentially waterborne disease notification rates

The campylobacteriosis notification rate in 2018 was 132 (128–135) per 100,000 people (6,463 notifications). Year-on-year, the notification rate has mostly trended downwards since 2009. The notification rate in 2018 was tied approximately equal lowest with 2015: 128 (124–131) and 2017: 128 (125–131) since reports began in 2001 (Figure 1).

A campylobacteriosis outbreak in Havelock North likely explains the increase in 2016.

The large decrease in the campylobacteriosis rate from 2008 onward (Figure 1) has been attributed to the introduction of food safety regulations for poultry production in 2007 and 2008 [1].

Figure 1: Campylobacteriosis notification rate, 2001–2018

Fig1

Source: [2]

In 2018, the age-standardised notification rate for giardiasis was 31 (29–33) per 100,000 people (1,392 notifications). The rate has remained unchanged from 2015 (Figure 2).

The age-standardised notification rate for cryptosporidiosis was 38 (36–40) per 100,000 people (1,551 notifications) in 2018.  The rate marks an increase from 2014 and it is now approximately equal highest with 2001:  35 (33–37) (Figure 2).

Improvements in diagnostic testing partly explain changes in potentially waterborne disease rates. Across New Zealand, there has been a gradual shift to culture-independent diagnostic testing (CIDT) for enteric diseases. CIDT tests for several enteric diseases simultaneously, which has resulted in improved detection rates [3].

Figure 2: Cryptosporidiosis and giardiasis notification rates, 2001–2018

Fig2

Source: [2]

In 2019, there were 537 notifications of campylobacteriosis, 211 notifications of giardiasis, and 140 notifications of cryptosporidiosis that reported drinking untreated water during the incubation period. 

However, risk factor information was only collected for a proportion of notifications, so these numbers may be an underestimate.  Risk factor information was collected for only 30.6% of campylobacteriosis notifications, 41.9% of giardiasis notifications, and 41.6% of cryptosporidiosis notifications.  Risk factor completion rates varied substantially by District Health Board.  

In 2015–19, the following District Health Boards (DHBs) had higher rates of campylobacteriosis, giardiasis and/or cryptosporidiosis with a risk factor of drinking untreated water:
- Hawke's Bay DHB
- Northland DHB
- Wairarapa DHB
- Tairāwhiti DHB 

However, low completion rates for risk factor information in many DHBs suggest the rates presented in the 'Notifications of potentially waterborne disease with recreational water as a risk factor' factsheet are likely to be underestimates (Figure 3a-c).

 Figure 3a: Risk factor completion rate for campylobacteriosis notifications, by DHB, 2015–19

  Fig4 v3

 Figure 3b: Risk factor completion rate for cryptosporidiosis notifications, by DHB, 2015–19

 WBD_DW_CryptoCR

 Figure 3c: Risk factor completion rate for giardiasis notifications, by DHB, 2015–19

 WBD_DW_GiardiaCR

Source: [4]

References

  1. Duncan, G. 2014. Determining the health benefits of poultry industry compliance measures: the case of campylobacteriosis regulation in New Zealand. New Zealand Medical Journal 127(1391): 22–37.
  2. ESR. 2018. Notifiable diseases EpiSurv data extraction. Porirua: Institute of Environmental Science and Research Limited. (personal communication with ESR Senior Analysts)
  3. New Zealand Food Safety. 2019. Annual report concerning Foodborne Disease in New Zealand 2018. Ministry for Primary Industries
  4. ESR. 2020. Notifiable diseases EpiSurv data extraction. Porirua: Institute of Environmental Science and Research Limited. (personal communication with ESR Senior Analysts)
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