Among parents, you often hear these four words: “Kids are germ factories.”

But a new study out of Drexel University’s Dornsife School of Public Health found that while you might think bringing more day care facilities to your block might make you and your neighbors sick more often, that doesn’t appear to be the case.

Neal D. Goldstein, PhD, assistant research professor, led a team that looked into the density of day cares in Philadelphia and compared them to areas where cases of whooping cough occurred in the city.

“Hypothetically, more day care use could translate to more children, parents and caretakers getting sick because of everyone being in contact with each other. But we wanted to ask the question, ‘Do these people carry germs back into the local community, making other kids sick?’” Goldstein explained. “The answer to that appears to be, ‘No.’ The presence of day cares in an area does not necessarily mean there is community risk of pertussis among kids.”

However, numbers gathered for the study — which Goldstein and co–authors Loni Philip Tabb, PhD, and Seth Welles, PhD, of Drexel, and E. Claire Newbern, formerly with the Philadelphia Department of Public Health, published in Public Health — shows that vaccination is still the most important factor when fending off whooping cough.

In a large control group of Philadelphia children who were included in the study because they did not contract pertussis, 81 percent were current on their immunization against the illness. Among the group studied because they had contracted pertussis, just 64 percent were immunized.

“The most important factor we observed that was correlated with greater pertussis risk was lack of vaccination,” Goldstein said. “We know that vaccination is important, but this analysis suggests that it’s even more important than where you live.

The researchers looked at reported cases of pertussis in Philadelphia among children up to age six from 2001 through 2013 — which amounted to 410 — and mapped them against registered day care sites — roughly 2,000 in the city. To measure density, the team broke out the city’s neighborhoods and assessed how many day care sites there were per square mile. They then overlaid these data with the number of pertussis cases also occurring in each neighborhood.

Data in the study did not show any correlation between higher densities of day care facilities and elevated prevalence of pertussis.

Goldstein said the lack of correlation between day cares and pertussis could come down to Pennsylvania’s strict vaccination requirements for children in day care.

“This vaccination requirement should provide a base level of protection among children — and adults — provided that people have received the vaccine,” he said. “Granted, these vaccination requirements can be exempted out of for medical and nonmedical reasons, but, hopefully, there are sufficient numbers of vaccinated children — and workers — to cancel out any affects of those who aren’t vaccinated.”

Varying levels of pertussis were found, regardless, in the city’s different neighborhoods. While the city–wide average was six cases per neighborhood during the study time period, the South Broad–Girard Estates neighborhood showed 24 cases, with two nearby neighborhoods also having more than 10 cases. In the meantime, Center City, Fairmount–Spring Garden and Sharswood–Stanton at the center of Philadelphia and Overbrook Park–Wynnefield Heighs in the west each just had three cases.

Some additional reasons for the lack of correlation between day cares and pertussis could include unregistered day cares that the study didn’t take into account, as well as the fact that people might not use day care in their immediate neighborhood. For instance, parents might use a day care closer to their job.