Epidemiologists to test sewage in Karachi for presence of coronavirus and its concentration

Public health researchers are set to evaluate the feasibility of a faster way to detect new cases of Covid-19 in Karachi, according to a statement issued by the Aga Khan University on Tuesday.

Infectious disease epidemiologists from the Aga Khan University, the National Institute of Health, Islamabad, and the World Health Organisation’s Pakistan Office will collaborate with Karachi’s District Health Office, East, to pilot a sewage surveillance system that will regularly test wastewater samples for the presence of the coronavirus and its concentration.

They are building on work by health authorities in several countries such as the US, Canada, Australia and several European nations to set up extensive sewage surveillance systems. These systems have helped detect high concentrations of the virus in sewage a week to ten days before cases would rise, enabling public health authorities to take prompt action to contain the spread of the disease.

Sewage surveillance systems take advantage of the fact that the presence of viruses can be identified in sewage before a person shows symptoms. For example, people can shed SARS CoV-2 in their stool in the first three to seven days after infection, long before a person begins to suffer from a fever, cough or shortness of breath. This means that wastewater sampling has the potential to act as a sensitive, early warning system for trends in new cases and a potential way to prevent new cases. That’s because nasal swab tests, which detect the presence of the virus in the nose, are typically only taken after symptoms appear, between seven and ten days after infection, which means that people could have unknowingly been spreading the disease for days before their positive test.

Researchers will analyse the amount of SARS CoV-2 particles per millilitre of filtered sewage to estimate the number of cases in the area. They hope to generate data that will help them estimate the future number of cases in a well demarcated catchment area by measuring viral concentration in sewage samples.

If analysis of sewage samples shows a continuous increase in the presence of SARS CoV-2 particles, then this could predict an uptick in cases before COVID-19 nasal swab test results become available, thereby giving public health departments and hospitals advance notice of a surge in cases.

Data about the quantum of the virus in wastewater will also be compared with records from the district health office about the number and location of positive tests in the area to prepare heat maps of high and low incidence areas. This could enable prompter preventive measures such as mass testing or targeted lockdowns to be taken in high-burden areas. Conversely, the data could also help provide an indication of a forthcoming decline in new cases which could inform policy decisions such as the easing of restrictions.

“Insights from sewage surveillance can help us get ahead of the virus and take more effective measures to curb new cases,” said Dr Imran Nisar, assistant professor at the AKU and principal investigator of the study. “No one knows when this pandemic will end, but new tools such as wastewater analysis can potentially make mitigation measures more effective.”

Researchers also plan to compare data about the number of vaccinations in the area against the volume of cases to understand the effectiveness of vaccine drives.

In later phases of the project, researchers will conduct genetic sequencing of wastewater samples to determine whether new Covid-19 variants have arrived in the city. This could signal the need to ramp up prevention measures or consider changes in precautionary measures, treatments or vaccine roll-out plans.

“Lockdowns have enormous social and economic consequences,” said Dr Nisar. “Comparing data from our sewage surveillance study with clinical and epidemiological data from the community will enable us to halt the cycle of surges leading to lockdowns by enabling policymakers to take prompter, more effective decisions. Throughout the study, we’ll be working closely with the district health office to ensure timely use of data.”

Once researchers have assessed the feasibility of the system in Karachi, they hope to be able to scale up the programme at the provincial and national level. The initiative has been funded by Program for Appropriate Technology in Health, USA and the Bill & Melinda Gates Foundation, USA.