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Exactly when SARS-CoV-2 virus first spilled over - likely from bats, to either a human or an intermediary host - remains the subject of considerable debate. While we only learned of the Wuhan outbreak in late December, we've seen studies suggesting that first species jump may have occurred somewhere in China several months earlier (see Evolution and molecular characteristics of SARS-CoV-2 genome).
The assumption, at least until a few days ago, was that the virus was carried from Mainland China to Europe by infected travelers, likely in mid-to-late January.
Italy, the first hard hit country, reported their first locally acquired case on February 21st (see Italy Reports 1st Locally Acquired COVID-19 Case (Possibly 2 Others)). Within a week, Italy would discover more than 1,000 new cases (see Italy: MOH Announces 228 Additional COVID-19 Cases (n=1049)).
Late this week, Italy's National Institute of Health announced that a limited number of waste water samples had retrospectively been tested for traces of the SARS-CoV-2 virus - and that samples from two municipalities (Milan and Turin) collected on 12/18/2019 - tested positive for the virus.
While more details will be published soon by the ISS (Istituto Superiore di Sanità), we have the following (translated) press release to ponder:
SS study on waste water, in Milan and Turin Sars-Cov-2 already present in December
ISS, 18 June 2020 - Traces of the SARS-CoV-2 virus already existed in the waste waters of Milan and Turin in December 2019. A study was soon to be published by the Istituto Superiore di Sanità carried out through the analysis of waste water collected in times prior to the occurrence of COVID-19 in Italy. The samples taken in the purifiers of urban centers in northern Italy, were used as a "spy" of the circulation of the virus in the population .
"Since 2007 with my group * we carry out research in environmental virology and collect and analyze samples of waste water taken at the entrance of purification plants" explains Giuseppina La Rosa of the Department of Water Quality and Health of the Department of Environment and Health of the Istituto Superiore di Sanità, which conducted the study in collaboration with Elisabetta Suffredini of the Department of Food Safety, Nutrition and Veterinary Public Health.
“The study - continues La Rosa- examined 40 wastewater samples collected from October 2019 to February 2020, and 24 control samples for which the sampling date (September 2018 - June 2019) allowed to safely exclude the presence of the virus. The results, confirmed in the two different laboratories with two different methods, showed the presence of SARS-Cov-2 RNA in the samples taken in Milan and Turin on 12/18/2019 and in Bologna on 01/29/2020. In the same cities, positive samples were also found in the following months of January and February 2020, while the samples of October and November 2019, as well as all the control samples, gave negative results ".The detection of viruses in waste water (or raw sewage) is nothing new, and testing is routinely done in many parts of the world looking for evidence of polio, which is shed copiously in feces. We've looked at this surveillance system before (see Polio Virus Detected By Environmental Surveillance In Egypt).
This research may help to understand the beginning of the virus's circulation in Italy and provides information consistent with other results obtained from the retrospective analysis on samples of hospitalized patients in France, which identified a SARS-CoV-2 positive in a respiratory sample , therefore clinical, dating back to the end of December 2019, and to a recent Spanish work that found SARS-CoV-2 RNA in waste water samples collected in mid-January in Barcelona, about 40 days before the notification of the first autochthonous case ".
“Our results - underlines Luca Lucentini, director of the Water Quality and Health Department - confirm the consolidated international evidence on the strategic function of monitoring the virus in samples taken regularly in the sewers and at the entrance to the treatment plants, as a tool capable of identifying early and monitoring the circulation of the virus in the various territories, supporting the fundamental information of integrated, microbiological and epidemiological surveillance. It should be noted that the discovery of the virus does not automatically imply that the main transmission chains that led to the development of the epidemic in our country originated from these first cases, but, in perspective, a surveillance network in the area may prove to be valuable to control the epidemic.
"Moving from research to surveillance - continues Lucentini - it will be essential to arrive at a standardization of methods and sampling since the positivity of the samples is affected by many variables such as, for example, the sampling period, any meteorological precipitations, the emission of waste from industrial activities which can affect the results of activities to date conducted by different groups. We work to give the country a surveillance network together with Arpa and Ispra ".
"In this sense - concludes Lucia Bonadonna , director of the Department of Environment and Health of the Istituto Superiore di Sanità - we have presented a proposal for action to the Ministry of Health for the launch of a surveillance network on SARS-CoV-2 in wastewater , and as early as next July we will launch a pilot study on priority sites identified in tourist locations. Based on the results of the pilot study, we hope to be ready for surveillance on the whole national territory in the potentially most critical periods of next autumn ".
* Marcello Iaconelli, Giusy Bonanno Ferraro, Pamela Mancini and Carolina Veneri
Since samples are generally stored after testing, many countries have the ability to re-test them for traces of SARS-CoV-2.
All of which should provide us with a much better picture of the global spread of the virus, even before the first cases were detected by regular surveillance.
