Coronavirus cases continue to mount in San Diego County while 30 other reported communicable diseases waned the first half of this year, according to a monthly county report. Local health experts say stay-home orders during the pandemic likely curbed behaviors that contribute to infections but that fear of contracting the virus may have kept patients from seeking care.
Dr. Eric McDonald, medical director of the county’s Epidemiology and Immunization Services Branch, said a decline in highly contagious diseases like pertussis and mumps aligns with the timing of stay-home orders.
Both had been on the rise in the county prior to the pandemic, McDonald said.
“They both dropped like a rock ever since we stopped interacting with each other because of the lockdown from COVID, and so we definitely benefited with those diseases,” McDonald said in a phone interview Friday.
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The county’s monthly report published last week shows more than 100 fewer cases of pertussis, or whooping cough, so far in 2020 than this time last year. Monthly cases dropped from 41 in March, when the stay-at-home order was implemented, to 10 in April. A total of seven cases were reported in May and June.
Mumps cases did not shrink as significantly. San Diego County reported 19 cases at this point in 2019 compared to 16 this year. Only a couple of cases were reported in January but that jumped to 10 in February and has since declined to a total of 4 in March and April. No cases were reported in May and June.
The county this year also reported far fewer chronic cases of hepatitis C — only 1,483 cases were reported in the first six months of 2020 compared to 2,188 for the same period last year. Dr. Martin Hoenigl, an assistant professor at UC San Diego's School of Medicine, said the decrease was actually worrisome.
“I think the most important reason for the drop in diagnosed communicable diseases in 2020 compared to 2019 is the fact that people are not presenting to care, and therefore don’t get diagnosed at an early stage,” Hoenigl said in an email.
The infectious disease researcher said UCSD usually diagnoses up to 700 new cases of hep C a year but that and testing has dropped by a third, noting a similar slump in emergency department visits.
“Importantly, hospitals and healthcare settings are safe — also during the current times of the pandemic — and people should access them if they need them,” he said.
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The county reported reductions in vector-borne illnesses, which are already low each year, and enteric diseases as well. These types of illnesses are often linked to travel; While outside the region, a person may contract an illness from a mosquito or tainted food or water and then be diagnosed after returning home to San Diego.
The decline is not unexpected because fewer people are traveling but McDonald said downward trends in diseases like salmonellosis or shigellosis are not uncommon mid-year.
“They tend to go down at this time of the year anyway and then they start increasing as the late summer early fall comes along so, I’m not sure whether that decrease is significant, but if you compare it year to year from the year before, we’re certainly down,” McDonald said.
County Department of Environmental Health vector ecologist Chris Conlan said the county’s dip in monthly cases of dengue fever and Zika is also likely linked to a lack of vacationing during COVID because those illnesses aren’t known to be carried by local mosquitoes.
“People aren’t now journeying to places like Mexico or Asia or places where dengue is more active — they’re not coming back with it and so you’re seeing a lot fewer cases,” he said.
There have been no reported cases of Zika this year and two instances of dengue. Last year at this point those figures were three and five, respectively.
However, the region reported six cases of malaria so far in 2020 — four more than over the same time frame last year.
There have been no cases of West Nile virus reported this year, but Conlan said that disease is seen in local mosquitoes. However, a surge hasn’t hit San Diego since 2015, when more than 40 cases were reported.
Conlan said years can pass in between outbreaks.
“It’s been quiet — now that’s not to say it can’t take off once it gets going, but fingers crossed, we seem to be doing OK so far this year,” he said.
Conlan said a batch of the buzzing pests has tested positive for West Nile this year. He encouraged San Diegans to use their time at home to review the surrounding area for standing water, even in small containers.
Conlan said an invasive species that thrives in backyards and urban settings moved into the county about six years ago, which may explain why residents are noticing their presence more so during the pandemic.
The county did not report year-to-date reductions for six diseases.
Compared to the first half of 2019, cases of acute hepatitis A were up by three for a total of 13 and malaria cases increased from two to six. There was one case each of Rocky Mountain spotted fever and chikungunya when this time last year there were none.
For two other diseases, case counts were the same for both time periods.
