We saw better-than-expected sequential improvement from quarter to 2 quarters and from quarter 3 to quarter 4.
Quarter four revenues totaled $711.2 million, which represents an increase of 2.3% as compared to the prior year period on a constant currency basis.
Growth in the quarter was aided by 2 additional selling days, which we estimate contributed approximately 3% points.
Excluding the impact of the additional selling days, we estimate that our constant currency revenues declined approximately 1%.
The days adjusted declines reflect continued recovery progression relative to the 4% decline we experienced during the third quarter of the year and the 12% decline we experienced during the second quarter of the year and it was ahead of the expectations we had at the time of the third quarter earnings call.
During the fourth quarter, we estimate that headwinds associated with COVID-19 caused a net negative impact of approximately $61 million or approximately 9%.
if we were to normalize for the negative impact, we estimate that our underlying business grew by approximately 11% on a constant currency basis, or 8% when normalizing for the selling day impact.
Quarter four revenue grew 2.3% on a constant currency basis and 4.4% on an as reported basis.
From a margin perspective, we had generated adjusted gross and operating margins of 58% and 26.6% respectively.
This translated into a year-over-year declines of 120 basis points at the gross margin line and 50 basis points at the operating margin line.
However, from a sequential standpoint, this represented an improvement of[Phonetic] AZ[/Phonetic] and 150 basis points respectively compared to quarter three levels.
On the bottom line, adjusted earnings per share was $3.25.
The Americas delivered revenues up $419.5 million in the fourth quarter, which represents an increase of 5% over the prior year period.
We estimate that the Americas would have grown approximately 12% excluding the impacts that COVID-19 had on the region.
EMEA reported revenues of $161.4 million in the fourth quarter, representing growth of 4.1%.
During the quarter, EMEA benefited from a one-time order of tracheostomy products and from the [Phonetic]extra [/Phonetic]selling days, the combination of which more than offset our estimated 1% COVID headwinds.
Revenues totaled $78.6 million in the fourth quarter, which represents a decline of 7.2%; however, we estimate that we would have had positive constant currency revenue growth in the mid-single digits, if not for the impact of COVID-19.
And lastly, our OEM business reported revenues up $57.7 million in the fourth quarter, which was down 6.9% on a constant currency basis.
Excluding the impact COVID-19 had, the business grew roughly 31%, which includes a benefit of approximately 13% from the acquisition of HPC.
Starting with Vascular Access, fourth quarter revenue increased 16% to $182.5 million.
We estimate that COVID-19 positively impacted the growth rates of our vascular products during the fourth quarter by approximately 5%.
Key drivers of revenue growth included PICC, which increased approximately 20%, CVCs which increased approximately 16% and EZ-IO which grew approximately 14%.
Moving to Interventional Access, fourth quarter revenue was $106.7 million or down 6.9% as compared to the prior year period.
We estimate that the recall and distributor issue impacted our business negatively by approximately $3 million.
In addition, we are pleased that Manta grew 33% globally in quarter four.
Now turning to Anesthesia, revenue was $86.1 million, which is lower than the prior-year period by 2.1%.
We estimate that COVID had an approximate 1% negative impact in the quarter, implying flattish performance on an underlying basis.
Revenues declined by 5.7% to $92.3 million driven by lower sales of our ligation portfolio.
We estimate a 9% headwind from COVID during quarter 4 indicating recovery as compared to the estimated 13% COVID headwind in quarter three.
Quarter four revenue increased by 5.3% to $93.9 million, which represents a new high watermark in terms of revenue dollars in any given quarter.
On a year-over-year basis, the business faced a difficult growth comparison but sequentially, it grew by 15% versus quarter three.
We estimate an approximate 28% COVID-19 related headwind during quarter four.
Additionally, we are encouraged that we trained approximately 130 new urologists in quarter four moving to a cadence that is consistent with our expectations prior to COVID and a positive leading indicator for future growth.
And finally, our other category, which consists of our respiratory and urology care products grew 6.1% totaling $98.1 million.
The strategic role of DTC is important as about half of the 12 million men being treated for BPH believe prescription medications are their only solution.
Key statistics include a doubling of brand awareness among men age 45 are higher post campaign versus pre-campaign levels.
Approximately 150% increase in visits to UroLift.com during the campaign and direct response numbers that exceeded our internal projections by a wide margin.
We have completed the market acceptance test and received positive feedback across more than 100 procedures completed by 20 urologists.
Regarding Japan, we remain on track for reimbursement decision in 2021 and view the approximate $2 billion addressable market as an incremental growth driver, that will be a positive catalyst for seeable future.
This is a prospective, single-arm IDE study of 150 patients across 13 sites to evaluate the performance of the entire range of Teleflex coronary guidewires and specialty catheters in chronic total occlusion percutaneous coronary intervention procedures, which is the most demanding PCI environment.
Once the study results are finalized, we anticipate updated labeling for our Guidewire and Specialty Catheter products which can address an estimated 100,000 CTO-PCI procedures.
We recently performed a market assessment update and still see a $100 million initial market opportunity for EZPlas.
One difference is that Z-Medica is growing into a $600 million addressable market while Vidacare is addressable market was closer to $250 million.
Z-Medica only reinforces our ability to get to those goals, and we remain committed to delivering constant currency revenue growth of at least 6% to 7% on an annual basis and reaching 60% to 61% and 30% to 31% adjusted gross and operating margins once we return to a more normalized environment.
For the quarter, adjusted gross margin was 58%, a decrease of 120 basis points versus the prior year period.
In total, we estimate that COVID negatively impacted our adjusted gross profit by approximately $44 million in the quarter.
As a result of the efforts, we estimate that operating expenses were reduced in the fourth quarter by approximately $13 million.
For full year 2020, we managed opex lower by an estimated $78 million.
Fourth quarter operating margin was 26.6%, were down 50 basis points year-over-year.
Net interest expense totaled $18.5 million, which is an increase of 10% year-over-year and reflects higher average debt balances versus the prior year period due to the acquisitions of HPC and Z-Medica.
Moving to taxes, for the fourth quarter of 2020, our adjusted tax rate was 10.1% as compared to 7.7% in the prior year period.
fourth quarter adjusted earnings per share declined modestly to $3.25 from $3.
28 a year ago.
Included in this result is an estimated adverse impact from COVID of approximately $0.55 and a foreign exchange tailwind of approximately $0.05.
In 2020, cash flow from operations was flat as compared to 2019 totaling $437.1 million.
At year-end, our cash balance was $375.9 million as compared to $301.1 million as of December 2019.
Over the course of the year, we deployed more than $750 million for external business development opportunities.
Inclusive of Z-Medica financing, we net leverage ended 2020 at [Phonectic]2.98 times[/Phonetic ], which remains well below our 4.5 times covenant.
Lastly from a selling day perspective, we will have 2 fewer selling days in the first quarter as compared to the year-ago period, we will have one additional day in the 4th quarter as compared to the year-ago period, and there will be no differences in the number of days during the second and third quarters.
In 2021, we project constant currency revenue growth between 8% and 9.5% as compared to 2020.
We also expect our Interventional Urology business to increase at least 30% over 2020 levels.
Additionally, Z-Medica is expected to contribute $60 to $70 million of revenue or approximately 2.5 points of growth.
We expect foreign currency exchange rates will be a tailwind to revenue growth of approximately 2%.
As a result, we expect our as-reported revenue to increase between 10% in 11.5% over 2020 and this would equate to $1 range of between $2.791 million and $2.829 million.
During 2021, we anticipate that adjusted gross margin will increase between 130 and 230 basis points to a range of between 8% and 59%.
We expect gross margin expansion will be driven primarily by a favorable mix of high margin products primarily, Interventional Urology as well as the acquisition of Z-Medica which will add approximately 50 basis points to gross margin.
During 2021, we anticipate that adjusted operating margin will increase between 110 and 210 basis points to a range of between 26% and 27%.
Given the relatively higher opex cost structure of Z-0Medica versus Teleflex, operating margin accretion from Z Medica will be less than the 50 basis points of gross margin accretion.
This slide serves as a bridge for our full-year 2020 adjusted earnings per share results to our full-year 2021 adjusted earnings per share outlook, beginning with the 2020 adjusted earnings per share of $10.67.
From an operating standpoint in 2021, we project additional earnings between $1.58 and $1.66 per share or an increase of approximately 15%.
Our 2021 earnings per share guidance also assumes the following: Foreign exchange is planning to [Indecipherable] for key currencies including a full year euro to dollar exchange rate of $1.21.
For 2021, foreign exchange is expected to provide a tailwind of approximately $0.35.
We now project Z-Medica to contribute between $0.21 and $0.26 of adjusted earnings per share in 2021, and this is an increase from our original expectation, which call for contribution of between $0.07 and $0.15.
In 2021, we expect interest expense to range between $63 and $65 million/.
The year-over-year reduction in interest expense is expected to contribute between $0.17 and $0.19 of earnings accretion if you would exclude the incremental financing costs for Z-Medica.
During 2021, we project that our adjusted tax rate will be in the range of 13.5% and 14% and will result in adjusted earnings per share headwind of between $0.33 and $0.38.
We estimate that weighted average shares will increase to $47 million for full year 2021 which is diluted by approximately $0.10.
Despite several headwinds, our adjusted earnings per share outlook of $12.50 to $12.70 is robust, representing growth of between 17.2% and 19% versus 2020.

Summary:
Quarter four revenues totaled $711.2 million, which represents an increase of 2.3% as compared to the prior year period on a constant currency basis.
On the bottom line, adjusted earnings per share was $3.25.
We estimate that COVID had an approximate 1% negative impact in the quarter, implying flattish performance on an underlying basis.
fourth quarter adjusted earnings per share declined modestly to $3.25 from $3.
As a result, we expect our as-reported revenue to increase between 10% in 11.5% over 2020 and this would equate to $1 range of between $2.791 million and $2.829 million.
Despite several headwinds, our adjusted earnings per share outlook of $12.50 to $12.70 is robust, representing growth of between 17.2% and 19% versus 2020.