Eighteen weeks after the local flu season began, the influenza virus is still sickening Clark County residents.
After several weeks of declining flu rates — with a low of 15 percent — positive flu tests spiked to 21 percent during the last two weeks. A positivity rate above 10 percent is considered evidence of an active flu season.
But health officials caution the jump doesn’t necessarily mean a flu resurgence.
“While this may partially reflect a true increase in influenza activity, a recent shortage of influenza tests may also be contributing to this elevated flu positivity,” said Madison Riethman, epidemiologist with Clark County Public Health, in an email.
The shortage has prompted health care providers to be more selective of whom they test, such as limiting testing to those most likely to have influenza, which could lead to an increase in the number of positive results, Riethman said.
The local flu season began in November and hit a peak in early January, when 44 percent of tests came back positive. That was the highest local positivity rate recorded since Clark County Public Health began tracking detailed data in 2014.
This flu season, Clark County Public Health has confirmed 14 influenza deaths — all among people with pre-existing conditions, including chronic lung disease, chronic heart disease, chronic kidney disease, diabetes and asthma. The local deaths include one child — a boy younger than 10 — and nine people 70 and older, according to data from Clark County Public Health.
Last flu season, Clark County had 26 flu deaths.
Flu activity remains elevated across the country, and the Centers for Disease Control and Prevention expects that trend to continue for several more weeks.
The vast majority of illness has been caused by influenza A H3N2 — a strain associated with more severe illness and hospitalizations. But last week, influenza B viruses were more frequently reported than influenza A viruses, according to the CDC.
Preliminary data suggests this year’s flu vaccine is 36 percent effective at preventing illness, according to the CDC.
Against the H3N2 strain, the flu vaccine is 25 percent effective. The vaccine was more effective — 67 percent — against another influenza A strain, H1N1. And it was 42 percent effective against influenza B viruses, according to the CDC.
Of the 14 Clark County residents who died from the flu, eight had received the flu shot.