This year, Mexico City has issued 8,072 more death certificates than the average for the same period in the past four years, according to a new study that suggests the country’s coronavirus death toll could be significantly higher than the official figure of nearly 7,400. Research published in the Mexican magazine Nexos on Monday used information from the capital’s 52 civil registries to estimate the number of death certificates created between 1 January and 20 May. The report’s authors, investigators Mario Romero Zavala and Laurianne Despeghel, found 37% more death certificates were issued in April 2020 than that month’s average during the previous four years. By the end of May they estimated the number would mushroom by 120%. The authors said not all those excess deaths were caused by Covid-19, but some of those who died “didn’t go to hospitals for fear of catching it” and died of other causes. Romero and Despeghel put the percentage of excess deaths officially attributed to Covid-19 in Mexico City at 25% – lower than the rates of 97% in Germany and 54% in the UK. As of Monday, Mexico City had recorded 1,963 Covid-19 deaths, according to its mayor, Claudia Sheinbaum. That is the highest tally of any Mexican state, but a figure that is coming under increasing scrutiny since the country’s rate of testing remains low. Mexico has now officially recorded 7,394 deaths and 68,620 Covid-19 cases. The investigation into Mexico City’s death certificates added to growing questions about the official Covid-19 death count in both Mexico and its capital. Sheinbaum and federal health officials deny any deliberate miscounting of the official figures. Mexico ranks near the bottom in testing among Latin American countries with just 99 tests per 100,000 residents as of 15 May. Romero, the report author, told the Guardian: “Given the low number of deaths reported in Mexico, one would assume that we are undercounting.” “Confirmed cases are highly correlated with testing. Given that correlation, if a country takes a strategy where they do very little testing, it’s safe to assume confirmed deaths will also be undercounted,” Romero added. Coronavirus tsar Hugo López-Gatell previously predicted Mexico would hit its peak number of Covid-19 cases during the first 10 days of May and estimated the death toll would peak at about 6,000. The country recorded 479 deaths on Friday – its highest daily total yet – although both López-Gatell and President Andrés Manuel López Obrador claim the Covid-19 curve has “flattened”. López Obrador, who has claimed to have “tamed” the coronavirus, is pushing ahead with plans to open the country in stages, despite the rising death toll.