Mesa's Cardon Children's Medical Center saw a record-breaking number of patients in January, confirming that influenza and RSV season is in full swing in the Valley.
RSV (respiratory syncytial virus) and influenza cases typically increase in January and February around the Valley.
Cardon reports it saw 1,000 patients last month, with about 70 percent of the patients diagnosed with RSV.
"We have opened overflow units to accommodate extra patients," Cardon hospital spokeswoman Lindsay Carrillo said.
Last week alone, the hospital saw 190 positive cases of pediatric RSV or flu in the emergency room.
Mercy Gilbert Medical Center reports it is seeing two to three times as many positive cases for RSV.
RSV infects the lungs and breathing airways. People of all ages may get RSV, which may look like a common cold. But for young children - and especially infants - it can cause serious problems because of the mucus it produces, which may hinder or block air passages.
Influenza is another respiratory disease that can make people feel miserable with cough, body ache and fever.
According to this week's report from the state Department of Health Services, influenza cases have been steadily rising since January and are higher than this time last year. This week's RSV figures match last year's.
The diseases may be more rampant in the public since most people who are sick don't end up being tested for the illnesses.
Unlike RSV, there is a vaccine for influenza. Health officials say the increase of influenza cases this year may indicate fewer people received the vaccine.
Both viruses are always around, but lay dormant until the weather turns cold and they thrive, said Sandy Marken, director of pediatric nursing for Cardon Children's Medical Center.
"As folks travel around for the holidays and go from one place to the next, then you see a surge in the virus, RSV in particular. It's on a journey to populate and grow and do as much damage as it can. And then as the weather starts to warm up, viruses get killed with heat," she said.
With the Valley seeing an ebb and flow of weather patterns this year - from the 60s and 70s one week to the 30s and 40s the next - it's entirely possible the viruses have not hit their peak, she said.
"Our prevention nurse is indicating that. We're not done yet," she said.
Most of the children in the hospital with RSV are very young and nearly half are younger than 1, she said.
"The younger the child, the higher the risk because their lungs haven't formed. They're not able to cough and get that congestion moving and out of their lungs and airways," Marken said.
In the hospital, medical providers can suction out the mucus from the babies and try to keep them hydrated.
Marken advises parents to get their children to a doctor if they have a persistent cough that lasts for several days. Children should also be seen if they experience a significant drop in energy level. Babies may struggle to nurse or take a bottle if they are having difficulty breathing or have blocked nasal passages.
"They also should not be going to a neighborhood house for a play date, or going to school and running a risk of exposing other schoolmates," she said.
Mesa Unified School District spokeswoman Kathy Bareiss said the district encourages parents to keep sick children at home to minimize the spread of illness and to receive care.
"Children should not come to school if they have the following symptoms: fever, diarrhea, vomiting, a severe sore throat or a draining wound," she wrote in an e-mail.