The number of rat complaints in Philadelphia are up from this time last year, but that may not mean rats are about to overrun the city.

The brown-haired rodents are on the mind of many after several rats were spotted feasting in the window of a popular Philadelphia brunch spot earlier this week. Photos and a video of the rodents went viral after they gained access to Green Eggs Café through a busted sewer pipe.

But does the disturbing sight feed the notion rats are on the rise in Philadelphia?

It’s not an easy question to answer.

Jeff Moran with the Philadelphia Public Health Department says there’s no measurement of the total rat population in the city. However, the department does record complaints from residents about rat infestations.

For the first four months of this year, more than 2,310 complaints were logged through Philadelphia’s rat hotline. That’s about 210 additional complaints than what they recorded for the same period in 2012, according to health department data.

In all of 2012, 8,503 rat complaints were filed with the health department. That’s 217 more reports than in 2011.

Moran says the numbers fluctuate as the seasons change, with a higher number of reports coming in during the warmer months.

Sewers are typically the most conducive home for rodents living in urban areas with the Norway rat being the most common species, according to the National Pest Management Association (NPMA).

NPMA spokeswoman Ela Voluck says the rats can squeeze through a space as small as a quarter, tread water for three days and survive being flushed down the toilet. They’ve been known to spread diseases like salmonella, jaundice and the plague through bites and their droppings.

The trade group says urban rats usually overrun the sewage system first and when that space becomes cramped, they move above ground to find food and space.

Philadelphia may see a higher number of rat reports this year thanks to the impending cicada invasion. Billions of the insects are set to crawl out of the earth along the East Coast after 17 years underground -- possibly providing added food to the rats.

In 2004, officials in Arlington and Alexandria, Virginia found anecdotal evidence that the local rat population increased during the time the cicadas were above ground. They also found rats that year were larger.

A staff of 22 people work in the health department’s Vector Control unit. Moran says when a citizen calls the city’s rat complaint line, staffers go out to the property in question and investigate.

If needed, the workers leave bait for the rodents. Moran says they also recommend repairs to properties that will cut off access to the rats and advise on trash storage and disposal. Workers also make minor repairs, at times.

Moran says Philadelphia businesses are required to have a rodent control plan to operate.

Philadelphians can report rat problems by calling 215.685.9000.

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Contact Vince Lattanzio at 610.668.5532, vince.lattanzio@nbcuni.com or follow @VinceLattanzio on Twitter.