Monitoring the health effects of climate change

This section describes statistics on three climate-sensitive infectious diseases in New Zealand: giardiasis, cryptosporidiosis and salmonellosis.

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Climate-sensitive disease indicators

Climate change has been described as “the biggest global health threat in the 21st century” [1].

Studies show that cryptosporidiosis and giardiasis (gastro-intestinal ‘tummy bug’ infections) are affected by rainfall patterns. Cryptosporidiosis and giardiasis can be caught by drinking water that has been contaminated with cryptosporidium and/or giardia cysts. High rainfall events can wash cysts from fields into water sources [3]. Drought conditions can lead to a greater concentration of cysts in rivers due to low water flow and volume [2].

Higher temperatures are linked to an increase in salmonellosis notifications. Salmonellosis (gastro-intestinal ‘tummy bug’ infection) can be contracted by eating or drinking food and/or water that has been contaminated by humans or animals with the Salmonella bacteria. An increase of 1°C in monthly average temperatures has been associated with 15% more salmonellosis notifications in that month [4].

No increasing trend for cryptosporidiosis and giardiasis notification rate

The age-standardised rate of giardiasis notifications steadily decreased from 2001 to 2006, then increased until 2010 (Figure 1). Since 2010, the age-standardised notification rate has decreased from 45 per 100,000 people to 32 per 100,000 people in 2016.

For cryptosporidiosis, the age-standardised notification rate has fluctuated since 2001, with a high rate in 2013 (34 per 100,000 people) (Figure 1).

Overall, giardiasis and cryptosporidiosis age-standardised notification rates currently do not show an increasing trend.

Figure 1

In the 10-year period 2007-2016, the highest age-standardised rates of giardiasis notifications were in rural parts of the South Island (Figure 2).

Figure 2: Giardiasis notification rate, by Territorial Authority (TA), 2007-2016, age-standardised rate per 100,000 people

 

In the 10-year period 2007-2016, the highest age-standardised rates of cryptosporidiosis notifications were in rural areas, particularly in the bottom half of the South Island and the Waikato region of the North Island (Figure 3).

Figure 3: Cryptosporidiosis notification rate, by Territorial Authority (TA), 2007-2016, age-standardised rate per 100,000 people

Salmonellosis notification rate is decreasing

The age-standardised rate of salmonellosis notifications peaked in 2001, followed by a sharp drop between 2002 and 2004, which is thought to be primarily due to improved food safety [4]. Notifications continued to decrease from 2005 onwards but at a much slower rate.

Overall, the rate of salmonellosis notifications has decreased over time (Figure 4).

Figure 4

In 2007-2016, the highest age-adjusted rates (per year) of salmonellosis are in the lower part of the South Island (Figure 5).

Figure 5: Salmonellosis notification rate, by Territorial Authority (TA), 2007-2016, age-standardised rate per 100,000 people

Effect on vulnerable populations

There is some overlap between regions with high rates of giardiasis notifications and high number of days of soil moisture deficit (hyperlink), namely Hawke’s Bay (Central Hawke’s Bay and Hastings TA) and the north-east top of the South Island (Kaikoura and Marlborough TA). Hawke’s Bay has several vulnerable populations including old and young people, who tend to be more susceptible to infectious gastro-intestinal diseases.

The highest rates of salmonellosis notifications tend to be in different regions from those with high numbers of hot days and populations vulnerable to infectious gastro-intestinal diseases. Rather, the highest rates of salmonellosis are often in regions that experience high numbers of cold days. One exception to this is Central Otago, which shows high rates of salmonellosis, a high number of hot days as well as cold days, and has a moderate size older population over 85 years.

Ongoing monitoring of health effects of climate change is needed

Climate change trends occur over many years, so correspondingly long-term health data are needed to show changes in disease occurrence and severity due to climate change.

However, it is useful to have monitoring of the likely health effects of climate change in place, in anticipation of possible increases and changes in patterns of diseases. Monitoring data on aspects of the environment and vulnerable populations is also needed to sit alongside monitoring of health effects, as is data at the regional level.

Information about the data

Specific change over time corresponding with climate change cannot be shown as the common baseline period in climate change science is 1960-1990, for which comparable data is not available.

Notifications of cryptosporidiosis and giardiasis

Source: EpiSurv, ESR

Definition: This indicator presents giardiasis and cryptosporidiosis notifications. Notifications where the person was overseas during the incubation period have been excluded. Notifications only cover those people who visited a GP or hospital for treatment, and may therefore underestimate the disease rate. Rates presented are per 100,000 people (or 100,000 people per year for combined data over 10-year periods). Age-standardised rates have been presented where possible, to take into account the population age structures of different population groups. 95% confidence intervals have been presented as error bars on graphs.

Notifications of salmonellosis

Source: EpiSurv, ESR

Definition: This indicator presents salmonellosis notifications. Notifications where the person was overseas during the incubation period have been excluded. Notifications only cover those people who visited a GP or hospital for treatment, and may therefore underestimate the disease rate. Rates presented are per 100,000 people (or 100,000 people per year for combined data over 10-year periods). Age-standardised rates have been presented where possible, to take into account the population age structures of different population groups. 95% confidence intervals have been presented as error bars on graphs.

References

  1. Costello A, Abbas M, Allen A, et al. 2009. Managing the health effects of climate change. The Lancet 373(9676): 1693-1733. DOI: 10.1016/S0140-6736(09)60935-1 (accessed 4 December 2018).
  2. Lal A, Baker MG, Hales S, et al. 2013. Potential effects of global environmental changes on cryptosporidiosis and giardiasis transmission. Trends in Parasitology 29(2): 83-90. DOI: 10.1016/j.pt.2012.10.005 (accessed 5 December 2018).
  3. Britton E, Hales S, Venugopal K, et al. 2010. The impact of climate variability and change on cryptosporidiosis and giardiasis rates in New Zealand. Journal of Water and Health 8(3): 561-71. DOI: 10.2166/wh.2010.049 (accessed 5 December 2018).
  4. Britton E, Hales S, Venugopal K, et al. 2010. Positive association between ambient temperature and salmonellosis notifications in New Zealand, 1965-2006. Australian and New Zealand Journal of Public Health 34(2): 126-9. DOI: 10.1111/j.1753-6405.2010.00495.x (accessed 5 December 2018).