Two more cases of whooping cough have been confirmed in Montgomery County public schools, according to health officials, who now are reporting a total of 20 cases since an outbreak during the first week of school.

The new cases involve a student at Northwest High School in Germantown and a staff member at Rocky Hill Middle School in Clarksburg. There is no link between the new cases and a Pennsylvania summer camp associated with the late-August outbreak, said Mary Anderson, spokeswoman for the county’s Department of Health and Human Services.

“This number in a short period is in large part due to the camp situation,” Anderson said, noting that the county sees cases of whooping cough every year.

School officials have sent letters to parents at affected schools advising them of the diagnoses and asking them to be on the lookout for symptoms. Cases have been confirmed at 10 Montgomery public schools this school year.

Early symptoms of whooping cough, or pertussis, often include a runny nose and a cough. They typically surface seven to 10 days after exposure to the bacteria that cause the illness, but they might not show up for as long as three weeks. Coughing can grow more severe over time and include a whooping sound produced by the sharp intake of breath during fits of coughing.

The disease is most dangerous to infants and those with compromised immune systems. Most young children receive immunizations that include a pertussis vaccination, and a booster is recommended at age 11 or 12.

As with other Montgomery cases, the two new cases involve individuals who had been immunized. Health officials say the protective effects of such immunizations can wane.

Montgomery has now had 40 cases of whooping cough this year — the same as it had for all of 2013. In 2012, the county had a spike in cases — 78 in all — when numbers peaked across the country. In 2011, the county had 18 cases, and in 2010, it had nine.

The whooping cough outbreak has come at the same time that school and health officials have been scrambling to get seventh-graders immunized, in keeping with new state requirements for Tdap (tetanus, diphtheria and pertussis) and meningococcal vaccinations.

The number of seventh-graders who have not met the requirement has dropped markedly, to 67 students as of Thursday, according to Montgomery health officials. Schools have been working with families to get vaccinations and provide documentation.

As of next Monday, students without such proof will be excluded from school, said Dana Tofig, spokesman for Montgomery County Public Schools. The district is no longer eligible for a deadline extension, he said, because too few students are out of compliance.

“Our hope is that we’ll be down to zero by the end of the week, and this won’t be an issue,” he said.

Last Thursday, Montgomery counted 1,491 seventh-graders in need of proof of vaccinations. The number was down to 487 students Monday, and by Tuesday it had dropped to 185.