Westchester County officials say they are concerned about the largest spike in positive coronavirus tests since the end of the spring.

There were 497 new active cases of COVID-19 cases across Westchester County this week, including more than 100 new cases over the weekend for a single day positivity rate over 2%.

Officials say there are now nearly 900 active cases in the county.

Hospitalizations have almost doubled and there are more deaths over the last seven days than in the previous few weeks. Officials say the highest uptick is in more densely populated areas.

Westchester County Executive George Latimer explained what he's most alarmed about in a virtual news conference Tuesday. "If that higher number of active cases becomes a higher number of hospitalizations and a higher number of fatalities then we are looking at something very serious."

A big chunk of this week's cases stem from an outbreak at Iona College, where 74 students have tested positive and are in isolation.

Latimer says the largest upticks have been in more congested areas, including in Yonkers, which has seen a slight uptick.

Officials tell News 12, "The city of Yonkers is doing everything we can to minimize the spread of COVID-19 under the guidance of the state and county departments of health."

New Rochelle Mayor Noam Bramson said in part, "Any increase is concerning. We will continue working closely with public health authorities to monitor patterns, address outbreaks, such as the spike at Iona, and, above all, remind residents and business to act responsibly."

While nearly 500 new cases sounds alarming, Latimer says testing has gone up, which typically does result in a higher number of positive cases.

The percentage of tests resulting in a positive test has stayed in the range of 1%, aside from Sunday seeing just over 2%.

Latimer says his team is going to monitor the situation and will make appropriate decisions based on whether cases continue to go up or come down. "As the numbers go up that's the single biggest message. We need to continue to show discipline, and we need to double down on discipline."

Meanwhile, Rockland has seen a slight drop in COVID-19 cases particularly in the hotspots -- the county's positive rate dropped from four to two percent to start the week. In both counties, officials want to make sure that people aren't getting too complacent.