COVID-19 Mitigation Measures May Have Curbed Conjunctivitis Infections

Study results indicated that measures taken to stem the spread of COVID-19 may have also reduced rates of conjunctivitis, or pink eye.

Public health interventions implemented to stem the transmission of COVID-19 were associated with decreased search interest in nonallergic conjunctivitis (pink eye) and conjunctivitis-associated emergency department (ED) encounters, according to study results published in JAMA Ophthalmology. Taken together, the findings indicate a sustained population-wide decrease in infectious conjunctivitis throughout the study period, researchers said.

Acute conjunctivitis, a highly contagious and common disease, is estimated to account for 1% to 2% of primary care visits in the United States and is “transmitted through close personal contact, fomites, droplets in the air, and poor hand hygiene,” authors explained.

“The incubation period for adenovirus conjunctivitis is typically thought to be 5 to 12 days, although certain types of adenovirus have incubation periods of more than 2 weeks. Once a patient becomes symptomatic, they typically remain so for roughly 2 weeks,” they added.

Researchers hypothesized that the same measures taken to curb COVID-19 rates, like mask wearing, social distancing, travel restrictions, and an emphasis on hygiene, would also alter the dynamics of infectious conjunctivitis.

To test their hypothesis, investigators assessed Google trends data from February 2016 through February 2021 for conjunctivitis, corneal abrasions, floaters, and photopsias. The 3 latter terms served as controls representing commonly searched but nontransmissible eye problems.

Data from November 2020 were excluded from the analysis due to a transient increase in searches for COVID-19–associated pink eye regarding a US vice presidential candidate, researchers noted.

Electronic health record data on conjunctivitis-related ED visits were gleaned from the University of Washington from February 2015 to February 2021. Any diagnoses of allergic conjunctivitis were excluded; monthly diagnoses of corneal abrasions and posterior vitreous detachments (PVDs) served as negative controls.

Both datasets “were analyzed using a counterfactual control method with the objective of building a counterfactual model of what would have happened if there were no lockdowns or changes in behavior,” the authors said.

Analyses revealed:

  • A total of 1156 ED encounters with a diagnosis of conjunctivitis took place between January 2015 to February 2021.
  • ED encounters for nonallergic conjunctivitis decreased by 37.3% (95% CI, −12.9% to −60.6%; P < .001).
  • Encounters for corneal abrasion (1.1% [95% CI, −29.3% to 29.1%]; P = .47) and posterior vitreous detachments (7.9% [95% CI, −46.9% to 66.6%]; P = .39) remained stable after adjusting for total ED encounters.
  • Search interest in conjunctivitis decreased by 34.2% (95% CI, −30.6% to −37.6%; P < .001) after widespread implementation of public health interventions to mitigate COVID-19.

Previous investigations of measures aimed at reducing conjunctivitis rates have yielded mixed results. One study evaluating the impact of improved hand washing found that “46% of patients with culture-positive adenovirus conjunctivitis were also found to have virus on their hands, and thus handwashing in itself was ineffective at reliably removing the virus from contaminated hands,” researchers explained.

Another strategy focused on isolating patients with suspected cases of pink eye in waiting rooms and minimizing their time spent in clinics. These efforts resulted a reduced nosocomial infection rate from 48.4% of new cases to 22.7% in the first year and 3.4% in the 2 years following implementation.

Conjunctivitis internet searches did not drop immediately following the US lockdown in March 2020, but decreased around 2 to 3 weeks later, suggesting that the decrease in incidence of conjunctivitis cases seen in this study was from viral causes, the authors hypothesized.

In addition, COVID-19 may have had a confounding effect on the analysis, as infection could have resulted in conjunctivitis-like symptoms, marking a limitation to the study.

“Search metrics in conjunction with mobility data may provide quantifiable metrics of social distancing implementation in the future and a method of surveillance of infectious conjunctivitis,” the researchers concluded.


Ferres JML, Meirick T, Lomazow W, Lee CS, Lee AY, Lee MD. Association of public health measures during the COVID-19 pandemic with the incidence of infectious conjunctivitis. JAMA Ophthalmol. Published online November 18, 2021. doi:10.1001/jamaophthalmol.2021.4852