As the COVID-19 pandemic raged around the country in the summer of 2021, another virus—an endemic one spread by mosquitoes—thrashed residents of one Arizona county, causing a record-shattering outbreak that left 101 people dead, according to a study published today by Arizona health officials.
The virus is West Nile, which constantly lurks in hundreds of bird species in the US and spreads to humans via mosquito bites. Most people infected—about 8 out of 10—will have no symptoms. But the unlucky remainder will develop a nondescript illness with fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Fatigue and weakness from a symptomatic case can linger for weeks to months. A small fraction of the symptomatic cases will develop a serious, life-threatening neuroinvasive case, such as meningitis or encephalitis.
West Nile Virus (WNV) was discovered in the US in 1999 and first detected in Arizona in 2003, when just 12 cases were recorded. Since then, the state’s yearly totals have often been around 100 cases, with Maricopa County always claiming the lion’s share. The outbreak record was set in 2004, quickly after its discovery. That year, the state saw 391 cases, 355 of which were from Maricopa.
But, in the shadow of the coronavirus Delta wave in the summer of 2021, Maricopa’s WNV outbreak totaled a whopping 1,487 symptomatic cases—breaking the 2004 record by more than fourfold. It is the largest WNV outbreak recorded from any county in the country ever. Yet, the recorded number in Maricopa is likely a severe undercount.
Coinciding outbreaks
Of the 1,487 sickened, 1,014 (68 percent) were hospitalized and 956 (64 percent) developed neuroinvasive disease. All of the 101 deaths occurred in those with neuroinvasive disease. The median age of all cases was 66, and the median age of those who died was 79. There were an additional 78 asymptomatic infections found in routine blood-donation screening.
The huge share of neuroinvasive cases in the outbreak suggests that a massive number of cases went unrecorded. Previous case estimates indicate that for every one neuroinvasive case, there are between 30 to 70 non-neuroinvasive symptomatic cases. That would put the true case total between 28,700 and 67,000 in the county, which has a population of around 4.5 million.
It’s unclear what spurred the massive outbreak. But it’s likely to be explained by a confluence of factors. Arizona health officials speculate it could be related to increased rain, increasing temperatures that prolong WNV season in Arizona, recent population growth and housing development in Maricopa, and changes in health care-seeking behavior during the COVID-19 pandemic.
But awareness of WNV and the outbreak—among both residents and health care providers—appeared to be troublingly inadequate, indicating that officials have more outreach and awareness work to do. This is particularly important in times of multiple outbreaks. While the COVID-19 pandemic appeared to exacerbate the WNV outbreak, the WNV also exacerbated COVID-19 responses, sending 1,014 people to already overwhelmed hospitals. Health facilities anecdotally reported to officials that there were times when intensive care units hit capacity, half full with COVID-19 cases and the other half with WNV. Overall, though, WNV’s burden paled in comparison to that from COVID-19 in the county, which saw over 19,600 COVID-19 hospitalizations in the same span of 2021.
With both viruses here to stay, Arizona officials are working on ways to improve responses. “Analyses are underway to identify data thresholds for increased public and provider messaging on prevention, diagnosis, and testing,” they wrote. “Timely and coordinated mosquito and human case surveillance are critical to identifying outbreaks and guiding prevention efforts.”
https://arstechnica.com/?p=1935003