BENGALURU/NEW DELHI—India recorded more than 4,000 COVID-19 deaths for a second straight day on Thursday, while infections stayed below 400,000 for a fourth day, though the virus has become rampant in rural areas where cases can go unreported due to a lack of testing. Experts remain unsure when numbers will peak and concern is growing about the transmissibility of the variant that is driving infections in India and spreading worldwide. Bhramar Mukherjee, a professor of epidemiology at the University of Michigan, said most models had predicted a peak this week and that the country could be seeing signs of that trend. Still, the number of new cases each day is large enough to overwhelm hospitals, she said on Twitter. “The key word is cautious optimism.” The situation is particularly bad in rural areas of Uttar Pradesh, India’s most populous state with a population of over 230 million. Television pictures have …