Routine SARS-CoV-2 wastewater surveillance results in Turkey to follow Covid-19 outbreak

A global pandemic of Coronavirus Disease 2019 (Covid-19) caused by severe acute respiratory syndrome coronavirus 2 (SAR-CoV-2) declared by WHO in March 2019 is still ongoing. As of 13 ^th of December 2020, 70 million people were infected by SARS-CoV-2 and 1.5 million people lost their lives globally (WHO, 2020). Since March 2019, diagnosis of Covid-19 cases has been done through PCR test of samples from nasopharyngeal and throat swabs. However, in March 2019, it was reported that the faeces [1] and urine [2] of all infected people contain SARS-CoV-2. Later, numerous researchers [3-7] detected SARS-CoV-2 in faeces of both symptomatic and asymptomatic patients. Moreover, some studies [1,4,8-12] suggested the possibility of extended duration of viral shedding in faeces after the patients’ respiratory samples tested negative. In this respect, SARS-CoV-2 wastewater-based epidemiology (WBE), i.e., wastewater surveillance, aiming to estimate the distribution of asymptomatic and symptomatic individuals in a specific region has received worldwide attention. Various research groups worldwide [1, 13-54] have started SARS-CoV-2 detection in wastewater since WBE provides tracking whole population by testing a small number of wastewater samples in a specific region and can predict SARS-CoV-2 RNA in human faeces a few days to a week before onset of symptoms. This makes WBE quite economic tool for continual tracking of decreasing or increasing trend of the Covid-19 in a particular region. However, up to date, almost all of the WBE studies have been performed with samples from a few treatment plants. There was no reported nationwide wastewater surveillance study that has been integrated into a national Covid-19 management strategy by decision makers. Nationwide, SARS-CoV-2 surveillance studies have great potential to reflect the actual distribution of Covid-19 cases in a community by accounting not only symptomatic patients tested but also asymptomatic patients having no or mild symptoms and not been tested. As opposed to clinical surveillance studies, wastewater-based surveillance studies will reflect the number of cases in a community by testing one sample from a treatment plant serving this community instead of performing individual swab tests.

Turkey, which is among the few countries that started wastewater based surveillance studies at the early stages of pandemic is a leading country, performing a nationwide surveillance study. The distribution of Covid-19 cases throughout the country via SARS-CoV-2 measurements in influent, effluent and sludge samples of wastewater treatment plants (WWTPs) located in 81 cities through May 2020-June 2020 was conducted [36, 51, 52]. In June 2020, nationwide routine sampling through 22 regional identified cities has been started. However, from June to September 2020 all samples were detected negative due to problems with RT-pCR primer targeting RdRp gene of SARS-CoV-2 genome. Since September 2020, routine sampling from 22 cities of Turkey with 2 weeks sampling period (weekly for mega city Istanbul) has been continued and regional Covid-19 distributions have been reported as viral loads on color-scale maps. To the best our knowledge, this is the first routine nationwide surveillance study indicating Covid-19 distribution regularly using color-scale presentation on a map.