Incidence of Disease Occurrence

Zoe Pretorius

Global occurrence:

Globally, diarrheal diseases are recorded to be the second largest cause of death, with the most reported deaths being in children under 5 (Ngobeni et al., 2022).
The WHO states that over 300 million cases of giardiasis are reported annually (Cernikova et al., 2018).
The prevalence of giardiasis varies, with an estimated occurrence of 2%– 3% in developed countries, and a prevalence of up to 30% in low-income and developing countries (Cernikova et al., 2018).

Figure 4: License: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication

Incidence of reported giardiasis cases, by sex and age group

A 2011-2012 surveillance summary report, done by the CDC found that in a sample of 100 000 individuals, reported giardiasis cases were the highest among males aged 1-4 years. The highest number of cases for females was also recorded in the age group 1-4 years. Overall, giardiasis cases were higher for males in every age group (Centers for Disease Control and Prevention [CDC], 2015).

Figure 5: Average annual incidence rate* of giardiasis, by sex and age group — National Notifiable Diseases Surveillance System, United States, 2011–2012† (Centers for Disease Control and Prevention [CDC], 2015).

Figure 6: Giardia intestinalis parasites (CDC Public Health Image Library, image 3394, 2006)

At risk individuals:

Overall, giardiasis is commonly associated with any age groups that have close contact with potentially contaminated water, food, or surfaces. However, certain individuals are at higher risk, such as:

Young Children (0-5 years) - Particularly children that are exposed to daycare settings (Yaoyu & Xiao, 2011).
Adults (20-40 years) - Those that travel to areas with poor sanitation or are involved in outdoor activities such as hiking or camping, where they may consume untreated water (from a river) (CDC, 2024).
Elderly - Older adults with weakened immune systems are at risk, as well as those living in long-term care facilities (CDC, 2024).
Immuno-compromised - any individuals that are immuno-compromised, such as HIV+ people, or those undergoing chemotherapy, are at particular risk of contracting Giardia lamblia, and may experience more severe symptoms when infected (Yaoyu & Xiao, 2011).

Demographic factors:

Infection with Giardia lamblia strongly correlates with being exposed to poor sanitation, limited access to clean water, and poor living conditions.
The disease is prevalent in developing countries, specifically in rural areas.
Lower socio-economic status is linked to higher risk (Yaoyu & Xiao, 2011).

Seasonal trends:

Giardiasis peaks during the summer and early fall months. (Scorza & Lappin, 2023)
The higher incidence in warmer months is closely associated with increased recreational water use (Scorza & Lappin, 2023).
An increase can be seen in areas during rainy season, this can be due to increased runoff of the rainfall, which may contaminate water sources with faecal matter containing the Giardia cysts (Atherholt et al., 1998).
In tropical and subtropical regions, giardiasis can be more prevalent year-round, while in temperate regions, it might show more pronounced seasonal patterns.

Fiigure 7: Map of South Africa showing the study site, Prevalence and genetic characterization of Giardia lamblia in relation to diarrhea in Limpopo and Gauteng provinces, South Africa,"(Samie et al., 2020), Parasite Epidemiology and Control, Volume (9),. Copyright 2020 by Publisher.

Giardiasis in South Africa:

Although very few studies have been done on the prevalence of giardiasis in South Africa (SA), a study done in 2020 titled "Prevalence and genetic characterization of Giardia lamblia in relation to diarrhea in Limpopo and Gauteng provinces, South Africa" (Samie et al., 2020), looked at the prevalence of Giardia lamblia in 2 South African communities. The study involved Giyani, Limpopo (rural community) and Pretoria, Gauteng (urban community), to ascertain information on the spread and prevalence of the disease in South African communities.

The study found that infection prevalence was highest in Giyani at 11.9%, compared to Pretoria's infection rate of 4.5% (Samie et al., 2020). Further providing evidence that giardiasis has a higher incidence rate in rural areas as opposed to urban areas.

Figure 8: Rural population; obtained from: World Bank, 2023 (License : CC BY-4.0 )

This is significant in a South African context, because according to a World Bank rural population estimation done in 2023 (World Bank., 2023), 18 837 844 South Africans live in rural areas.
This number equates to 30.37 % of the total population. (Total = 62,027,503) (South African census, 2022)
This means that nearly a third of the population is at higher risk for infection due to their geographic location, the lack of clean water in the area, limited access to healthcare, etc.

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