As the number of Zika-virus-infected nations and jurisdictions around the world jumped to 30 Wednesday, four Boston public schools cancelled planned school trips to the Dominican Republic, Ecuador and Nicaragua.

Officials wouldn't say which schools or how many students involved but issued a statement: "Boston Public Schools is canceling a small number of field trips to countries where there is currently an outbreak of the Zika virus to protect the safety of students, staff, and families, and to prevent transmission to the Boston community. The district is not canceling all global field trips. These decisions were made after working with leaders at the impacted schools, and with the safety and wellbeing of our students, families, and staff being a top priority. The district and school leaders are working to find alternative destinations where possible and appropriate, and to ensure that students and families who need refunds receive them."

Dr. Anita Barry, director of the Infectious Disease Bureau with the Boston Public Health Commission, said school officials did not consult with her about the decision, but said it is understandable given some of today's realities.

"Sometimes in the teenage years," Barry said, "some young women may be pregnant, and of course it that were the situation, we certainly would advise them not to travel to countries where the zika virus is circulating" because of the risk of grave brain and skull damage from Zika to developing fetuses.

According to the Massachusetts Department of Public Health, females aged 15 to 19 in Boston gave birth to 318 babies in 2013, the most recent year with available data. The Boston teen birth rate of 12.2 per 1,000 was close to the overall state rate of 12.0.

Aside from the issue of pregnant girls and women, asked what advice she would give schools about whether to have students make trips to areas where mosquitoes carrying Zika have been reported, Barry said, "We're not aware that Zika virus would cause more severe disease in teenagers. In fact, only one out of five people who are infected with Zika get any symptoms at all, and usually they are pretty mild."

Spots checks with state school and teacher associations Wednesday indicated that Boston is one of a very few and maybe the only Massachusetts school district so far cancelling travel over Zika concerns. Elsewhere in the city, Boston College High School, which runs service trips to the Dominican Republic and Ecuador, is following the Zika concerns but has made no decisions about cancelling any trips, according to a school spokeswoman.

EF Education First, with a major office in Cambridge, runs educational tours to several Zika-infected countries, including Bolivia, Brazil, Costa Rica, the Dominican Republic, Ecuador, Nicaragua, and Panama.

EF spokesman Adam Bickelman said by email, "Given that the CDC [Centers for Disease Control] warning is very specific in nature, cautioning those that are or plan to become pregnant about the risks of travelling to the affected areas, we are not making any major changes to our tours at this time We are aware that Boston Public Schools is consulting with their student groups that are traveling to Central America to determine next steps on a case-by-case basis. However at this time no Boston Public School groups have officially cancelled their plans. We do have a few individuals from other school districts that fall under the CDC guidelines, and we are working with them on a case-by-case basis to determine a solution that works best."

Barry, the infectious disease chief, said, "For most students, it probably wouldn't be an issue, but for some other students who might be pregnant, it could really cause some really serious outcomes, birth defects in a baby. So I think you have to weigh the benefits and the risks there."

Airlines and cruise lines have offered various policies allowing pregnant women to cancel or reschedule trips if they have concerns about travelling to areas with reported Zika infections.

Travel Insured International said it’s seen a 30 percent increase from last year in the last month in sales of "cancel for any reason" travel insurance policies, which it attributed to people being concerned about cancelling a trip based on Zika concerns.

With videographer Justin Mintzes