Studies were eligible for inclusion if they focused on water sanitation and cryptosporidium within the USA and Brazil. The study search was based on articles published between 2020 and 2025. Studies were excluded if they used did not involve an evaluation of cryptosporidium and water quality within the USA and Brazil. In addition, studies that were more than 5 years old were not used in order to utilize up to date information on the subject matter. Preliminary research data showed that Brazil had high cryptosporidium rates due to subpar water sanitation, with very little data indicating cryptosporidium rates in the USA. A selection of the top 500 studies out of the 14,080 results found when a query was conducted were analyzed and a total of 384 out of the 500 studies were Brazil and cryptosporidium with water sanitization rates related while only 116 out of 500 studies were USA and cryptosporidium with water sanitization rates.

All search results obtained from Google Scholar, PubMed Central, and EBSCO databases were exported and compiled for screening. Duplicate records were identified and removed prior to the screening process. Following deduplication, all remaining records were screened based on title and abstract to determine relevance to the research question. Studies that met the inclusion criteria were then selected for full-text review. During the full-text review stage, articles were further evaluated for eligibility based on relevance to water sanitation practices and Cryptosporidium occurrence in Brazil and the United States. Studies that did not meet the inclusion criteria were excluded. A total of 15 studies were ultimately included in the final analysis. The number of studies at each stage of the selection process was documented to ensure transparency and reproducibility of the review methodology. This structured approach reduces selection bias associated with search engine ranking and improves the reproducibility of the systematic review.

The literature search was conducted using Google Scholar, PubMed Central and EBSCO database (Academic Search Ultimate) for Brazil research publications and for USA research publications. Search strings included a combination of terms inclusive of “cryptosporidium” AND/OR “water sanitation practices in USA” and “water sanitation in Brazil” AND/OR “cryptosporidium” as well as high cryptosporidium in “USA” AND/OR “water” in addition to terms related to cryptosporidium and water quality. PubMed Central a total of 3777 results were found; for Google Scholar, there were a total of 8050 results were found and for Academic Search Ultimate a total of 2253 results were found.

Furthermore, eligible articles were selected independently by each researcher based on abstract and title. Subsequently, each researcher independently verified the eligibility criteria and extracted the information in the available full texts. Where discrepancies existed, both authors met to resolve disagreements. Data was collected using an Excel spreadsheet and was based on cryptosporidium rates in various areas in Brazil and the USA.

Data was collected by researching which articles related to water sanitation and cryptosporidium occurrence in the USA and Brazil. A total of 15 articles were selected for this research. Articles that indicated a high prevalence of cryptosporidium as it relates to water sanitation in Brazil were selected and analyzed for their content. In addition, articles that were related to cryptosporidium rates and the USA were also selected. Articles that met the criteria were tabulated and included the name of the article, the author(s), the date of the article, a brief overview of the article and the relevance of the article to the research’s title. Initially, each article was reviewed by two individual authors for this research. Everyone worked independently to assess the usability of the article in relation to this research title. The articles that were selected for the purpose of the research were tabulated and included the name of the author, the date of the article, the author, an overview and a relevance to the research:

All studies were assessed independently by two researchers applying the Newcastle-Ottawa Scale adapted for cross sectional studies. This tool evaluates selection bias, performance bias, bias caused by inadequate control of confounding, and selective reporting bias.

RiskofBiasDomains—Figure 1

Figure 1. Risk of bias assessment across included studies using the adapted Newcastle-Ottawa Scale.

This section explains the four bias domains used to assess the 15 included studies. Each domain is scored as follows:

★★ = Low risk of bias/criterion fully or substantially met;

★ = Moderate/unclear risk of bias;

☆ = High risk of bias.

Leeway and benefit of the doubt are applied in some cases (e.g., if confounders are discussed narratively but not statistically adjusted, ★★ may still be awarded in descriptive/environmental studies).This four-domain adaptation prioritizes threats most relevant to waterborne pathogen surveillance and environmental epidemiology.Total score: Maximum 8 (★★ across all four domains = 8 points) (Figure 2).

Figure 2. Detailed reasoning by study. Prepared for: Cryptosporidium Systematic Review (Brazil vs. USA) Date: February 2026.

Most studies score 8/8 (low risk across all domains), with only Study 11 (Park, 2025) scoring slightly lower at 6/8 due to its narrative/historical format.

Notes on Park:

Park(2025)—MilwaukeeOutbreak

SelectionBias(★)

The study presents a historical case study centered on the Milwaukee outbreak, which reflects infrastructure and public health vulnerabilities present in many U.S. municipalities during the period. While the event is somewhat representative of broader national water system risks, it remains geographically and temporally limited. Because it is a single-event historical analysis rather than a multi-site comparative study, its external validity is constrained. Therefore, limited credit is appropriate.

PerformanceBias(★★)

The study provides a descriptive and analytical examination of environmental conditions, response measures, and systemic failures associated with the outbreak. Given that eco-disaster reviews often rely on retrospective data and narrative reconstruction, the methodological approach is appropriate for the context. While not experimental, the descriptive structure aligns with disaster analysis standards and supports internal consistency. As such, a moderate level of credit is justified.

BiasDuetoInadequateControlofConfounding(★)

Although infrastructure degradation, water treatment processes, and environmental conditions are acknowledged, the chapter does not fully adjust for or statistically control confounding variables such as socioeconomic disparities, concurrent public health pressures, regulatory oversight gaps, or seasonal pathogen variability. The analysis identifies contributing factors but does not systematically isolate their independent effects. As a result, residual confounding remains likely, warranting limited credit.

This systematic review evaluated recent literature (2020-2025) examining the relationship between water sanitation practices and the prevalence of Cryptosporidium in Brazil and the United States. The findings consistently demonstrate that deficiencies in sanitation infrastructure, wastewater treatment coverage, and monitoring practices in Brazil are associated with higher reported rates of Cryptosporidium contamination when compared to the United States. In contrast, the United States benefits from more centralized regulatory oversight, established enforcement of the Safe Drinking Water Act, and broader access to treated potable water, which collectively contribute to lower reported prevalence in most regions.

Despite infrastructure disparities, both countries continue to face risks related to aging systems, rural access limitations, and treatment resistance of Cryptosporidium oocysts. The evidence underscores that effective sanitation infrastructure, regulatory enforcement, environmental surveillance, and risk-based monitoring are critical components in reducing waterborne protozoan transmission.

Overall, the review highlights the importance of strengthening sanitation equity, expanding wastewater treatment coverage, and implementing robust microbial monitoring strategies—particularly in vulnerable and rural regions. Continued collaboration between regulatory agencies, investment in infrastructure modernization, and the application of quantitative microbial risk assessment methodologies will be essential to mitigate future outbreaks and protect public health.

A systematic search of Google Scholar, PubMed Central, and EBSCO databases identified a total of 14,080 records. Following the removal of duplicate records, the remaining studies were screened based on title and abstract for relevance to water sanitation practices and Cryptosporidium occurrence in Brazil and the United States.

During the initial screening phase, studies that did not meet the inclusion criteria—such as those focusing on non-waterborne transmission, unrelated pathogens, or non-comparable geographic regions—were excluded. The remaining studies were then subjected to full-text review to further assess eligibility.

After full-text evaluation, a total of 15 studies met the inclusion criteria and were selected for the final analysis. These studies included a combination of environmental monitoring studies, outbreak investigations, systematic reviews, and regulatory or policy-related analyses.

The selection process was conducted to ensure that only studies directly relevant to the research objective were included, while reducing potential bias associated with database ranking or availability.

The included studies were assessed using an adapted Newcastle-Ottawa Scale to evaluate selection bias, performance bias, confounding, and selective reporting. Most studies demonstrated low risk of bias across the assessed domains; however, several studies were assigned moderate risk ratings due to limitations such as localized sampling, incomplete control of confounding variables, and reliance on single-event or model-based data.

The distribution of studies across each stage of the screening process supports the transparency and reproducibility of the review methodology.

Based on the 15 articles selected, in comparison to the USA, Brazil’s does not have the same water treatment infrastructure, and this leads to less adequate sanitation services. In comparing water quality standards between the United States and Brazil, the main difference in the findings is that the USA has the benefit of having the Environmental Protection Agency (EPA) who sets national water quality standards that states then adapt to their specific needs. On the other hand, Brazil primarily relies on its National Water Agency (ANA) to establish water quality standards, which is not an agency that is as focused on environmental health as the EPA. Also, due to Brazil’s diverse geography, water quality standards are often adapted to specific regions based on local water conditions and needs. In recent years, the EPA has actively worked with the ANA to enhance Brazil’s water quality standards via study tours and webinars.

Brazil has the highest number of cases of cryptosporidium in Latin America. According to Rocha et al., 58% of households in Brazil had secondary cases of Cryptosporidiumparvum and 27% of those secondary cases had diarrhea [9]. However, water treatment systems in the Northeast state of Bahia are not well monitored for cryptosporidium at their catchment points or in the final water distributed to the population.

In northeastern Brazil, 10% of animals had Cryptosporidium in their stool specimens with 22% of drinking water sources containing Cryptosporidium oocyst [10]. Rocha et al. stated that additional factors such as living in densely populated areas with poor hygienic sanitary conditions increase the occurrence of Cryptosporidium. Multiple factors cause the release of Cryptosporidium oocysts. The perpetuation of Cryptosporidium can be exacerbated by the resistance of these oocysts to conventional water treatment processes inclusive of chlorination and filtration. This contamination is important to public health due to numerous at-risk populations.

Recently, waterborne outbreaks of cryptosporidiosis have been seen in numerous countries inclusive of Brazil [11]. Causative factors include inefficient water management, untreated surface water, inadequate sanitation and poor drinking water that does not meet standards established by specific legislation.

In 2020, only half of the Brazilian population had access to sanitation services with approximately 49% of wastewater being treated prior it being discharged into the environment [12]. In Brazil, the majority of people live primarily along the coast, especially in large cities like Rio de Janeiro and São Paulo. This means that even though the nation has a plethora of water resources overall, the water quality in these densely populated areas can be greatly impacted by pollution as a result of high population density [13].

In rural Brazilian areas, there is a significantly lower access to treated water in comparison to larger cities. These disparities mostly exist in the North and Northeast regions where there are usually untreated sources like springs and wells which then leads to higher rates of waterborne diseases as a result of limited access to sanitation facilities as well as inadequate treatment infrastructure [14].

The strength of this review is the selection of studies that clearly showed a prevalence of cryptosporidium occurrence based on poor water sanitation practices. The main limitation was a high homogeneity in the results of the studies, which limited the selection of articles used for the study.