Before revision:  At early times, at order of few days, the infection rate in the city is close to  constant probably due to the lack of means to detect infected individuals before infection signs are observedand at later times it decays approximately exponentially due to quarantines.
After revision:  At early times, at order of few days, the infection rate in the city is close to constant probably due to the lack of means to detect infected individuals before infection symptoms are observed. Then at later times it decays approximately exponentially due to quarantines.