Improving Cholera Control Through Better Testing

Cholera continues to be a significant public health problem in places where safe water and sanitation are not easily available. In Africa, a large number of people are at risk, with about 87 million living in areas with high rates of cholera. However, these numbers are likely underestimated because they mostly rely on reports from clinics, which do not always confirm cases with reliable lab tests.

Cholera cases can vary widely depending on the time and place. During the years 2010 to 2016, most cases in Africa came from less than 5% of the population, with many outbreaks concentrated in just a few countries. Even in regions with high cholera rates, the spread of the disease can be unpredictable, with some years experiencing continuous cases and others having breaks of several years. This inconsistency complicates the way health authorities monitor the disease, as they may need different definitions and ways to report cases based on various factors. When the spread of cholera and the reporting methods differ significantly, it becomes hard to implement effective disease control measures.

Research has shown that targeting cholera control efforts toward areas with a history of high cases can improve the effectiveness and cost-efficiency of these interventions. This is crucial for activities like vaccination, where limited vaccine supplies need to be directed to the most affected areas. However, many African countries facing cholera do not have robust surveillance programs to guide such targeting. Although there are systems for tracking cholera cases in clinics, the methods vary greatly, with differences in definitions, the quality of data, and how cases are detected. Furthermore, systematic lab tests to confirm Suspected cholera cases face hurdles due to a lack of resources.

In a study from 2010 to 2019, only a quarter of suspected outbreaks in Africa had laboratory Testing data available, and even fewer confirmed actual cholera cases. While rapid tests are becoming more popular for detecting cholera, their use is still relatively new, and there is a lot of variation in how well they work in different places. No global standards currently exist for how to use these tests for monitoring cholera cases effectively.

A recent analysis found that nearly half of the suspected cholera cases were indeed true cholera, but this figure can change greatly depending on where and when it was measured. Many suspected cases could be due to other illnesses that cause diarrhea. Therefore, using limited vaccine supplies primarily based on suspected cases might not be the most effective approach. Improving lab capacity for confirming cases would enhance the efficiency of vaccination efforts and increase their impact, while also reducing the number of vaccination sites required.

To better understand the potential impact of improved testing, researchers looked at cholera-affected areas in Africa where detailed Incidence estimates exist. They built a model to assess how changes in testing capacity could improve vaccination efforts. The model evaluated different scenarios based on how testing was conducted, the thresholds for vaccination, and the scale at which campaigns were carried out.

The researchers used existing estimates of cholera incidence from 2010 to 2016, refining these figures to smaller geographic areas. They assumed that these rates would remain stable in the coming years unless vaccination was modeled. They also accounted for the fact that not all suspected cases would be true cholera infections, using a statistical approach to estimate the actual cholera rates.

In terms of vaccine properties, researchers assumed that fully vaccinated individuals would have a direct protective effect that decreases over time. They estimated that a significant portion of the population would receive two doses of the vaccine in the targeted areas.

For the model, they examined various scenarios related to testing capacity and the thresholds used for targeting Vaccinations. In total, they simulated 18 different vaccination scenarios, plus one without vaccination.

Under different testing conditions, researchers observed how well the incidence rates matched actual cases. They considered three settings: low capacity (where only suspected cases were reported), decentralized testing (where tests were systematically conducted at local levels), and centralized testing (where samples were sent to national labs).

For administrative units where cholera rates exceeded certain thresholds, they assessed how vaccination targeting would work under these various testing conditions. The overall impact of vaccination campaigns was measured in terms of how many cases were prevented and the cost-effectiveness of these actions.

The findings showed that systematic testing significantly improved the efficiency of vaccination campaigns. When targeting high-incidence areas, campaigns using systematic testing (either decentralized or centralized) always performed better than those relying solely on suspected case definitions. In scenarios with a high incidence rate threshold, decentralized testing allowed a more focused delivery of vaccines, ensuring that most vaccinated people were in high-risk areas.

For example, when districts with high cholera rates were targeted under decentralized testing, many fewer doses were required while still preventing a significant number of cases. This approach also made the campaigns more cost-effective, with less money spent per averted cholera case.

In scenarios where testing was used, the testing costs were lower, allowing resources to be allocated more effectively. The results suggested that introducing systematic decentralized testing could dramatically improve the outcomes of vaccination campaigns by reducing costs and allowing for better tracking of cholera cases.

Comparing decentralized and centralized testing methods highlighted that both have their advantages. Centralized testing targeted fewer individuals but had slightly better efficiency. The decentralized approach, however, performed more tests, leading to more accurate positivity rates.

Despite the progress shown in the models, significant challenges still exist in implementing effective testing in many cholera-affected areas. Variability in access to healthcare, the quality of data, and the capability to perform tests all affect how well surveillance systems can function.

While cholera rapid tests are increasingly available, they have not yet received global approval and their use remains inconsistent. Improvements in testing practices and the development of better testing protocols are essential to expand the use of vaccines effectively.

Moreover, the model used average cholera incidence rates from previous years, which might not reflect current conditions accurately. Additionally, the model did not capture the variations in disease transmission caused by outbreaks or emergencies.

Strengthening surveillance systems has long been recognized as vital for effective vaccine targeting and monitoring progress. Recent updates to health organization guidelines emphasize using multiple factors, including positive test results, to decide where to allocate vaccination resources.

Investing in laboratory capabilities, training health professionals, and ensuring supply chains are in place are critical for developing effective cholera control measures. Improved testing not only supports better vaccination strategies but also strengthens overall public health responses to cholera and other diseases.