SALEM — In June, public health officials in Oregon said they could pinpoint many of the state’s new COVID-19 infections to outbreaks at nursing homes, food processing plants and a northeastern Oregon church.

But in the past few weeks that has dramatically changed: Large outbreaks have surfaced less frequently and public health officials say they’re increasingly struggling to identify the circumstances under which Oregonians are becoming exposed to the coronavirus.

The state’s latest weekly report of new infections reflects just that. It outlines the number of new infections across the state by ZIP code from July 13-19, the latest week for which data is available. For many parts of Oregon, the report offers no clues for why new infections are on the rise.

Recently, Contact tracers couldn’t identify the source of a record 48% of new infections. The Oregon Health Authority has said it needs to keep that figure below 30% to keep the virus at bay.

Here’s a ZIP code breakdown of where the virus spread in the highest numbers in the week July 13-19:

No. 1: 97838 — HermistonThis is the state’s viral epicenter, and the situation continues to worsen at an accelerating rate. This ZIP code recorded 212 new infections from July 13-19 — jumping from 629 known cases to 841 cases since the start of the pandemic. That’s a 33% increase in just a week.

This ZIP code, which encompasses the northeastern Oregon city of Hermiston, now has surpassed the Newport ZIP code of 97365 as the Oregon ZIP code with the most cases per capita — about 322 cases per every 10,000 people. That’s about nine times higher than the average per capita rate statewide, which stands at about 37 cases per 10,000 residents.

The biggest single contributor to the week’s explosive growth in 97838 appears to be 37 cases from a new outbreak at the nursing home Regency Hermiston Nursing and Rehab Center. One person has died.

Workplace outbreaks have been contributing to the numbers slightly. Fifteen people have fallen ill from a new outbreak at Good Shepherd Hospital. Ten new cases were traced to a new outbreak at the Walmart Supercenter store in Hermiston. An existing outbreak at the Walmart Distribution Center more than three miles away grew by eight cases, to a total of 23.

But much of the spread appeared to be out through what public health officials have deemed “sporadic spread.”

The rising number of cases in Hermiston was so concerning that Oregon State University tested 400-500 randomly selected people in the community this past weekend to better understand the prevalence of the disease there. The researchers also plan to test the city’s sewage system for the prevalence of the virus.

No. 2: 97071 — WoodburnThis ZIP code encompasses Woodburn and some rural lands around it. Cases here climbed by 69, to a total of 435.

This area is home to a number of agricultural facilities and workers, who are known to be disproportionately affected by the virus’ reach.

This ZIP code has 144 cases per 10,000 residents, about four times higher than the per capita rate across the state.

No. 3: 97914 — OntarioThis ZIP code sits just west of the Oregon-Idaho border. Infections here rose by 67 cases, to a total of 374.

Long-term adult care facilities appear to be driving some of the increase. An outbreak at Brookdale Assisted Living grew by seven, to 39 total cases. Three people have died in relation to that outbreak so far — two of them during the week July 13-19.

On top of that, an outbreak at the Snake River Correctional Institution grew by two cases, from 117 to 119. The Oregon Health Authority also reported a new outbreak of five cases at the Walmart Supercenter store in Ontario.

This ZIP code has 195 cases per 10,000 residents, about five times higher than statewide average.

No. 4: 97233 — Southeast Portland and GreshamThis area is making yet another appearance on this weekly list of ZIP codes with the most new infections in Oregon. The per capita rate of infections here, at 103 per 10,000 residents, is close to three times the state average.

No. 5: 97080 — Gresham

Cases here grew by 64 from one week to the next, bringing the total cases to 244. That’s an increase of about 36%. The per capita rate of infections in 97080 isn’t much higher than the statewide average, though — with about 55 infections per 10,000 residents here, compared to about 37 per 10,000 residents statewide.

No. 6: 97236 — Southeast PortlandThis ZIP code has made frequent appearances on the weekly list of most new infections in the state. Infections in 97236 grew by 50 over the week, reaching a total of 439. The per capita rate of new cases in 97236 is 107 per 10,000 residents, close to triple the statewide average.

No. 7: 97801 — PendletonNew infections here grew by 47, to a total of 192 since the pandemic began.

The northwestern edge of the Pendleton area’s 97801 borders the northeastern edge of the Hermiston area’s 97838, which is the state’s hottest coronavirus spot per capita. So given its close proximity, it’s no surprise that the Pendleton ZIP code is experiencing a surge in cases.

An ongoing outbreak at the Eastern Oregon Correctional Institution doubled from 14 to 28 from July 13-19. Cases at the Hill Meat Company grew by one, to 10 cases.

The prevalence of the disease in the Pendleton area still is relatively low compared to neighboring Hermiston. In the Pendleton ZIP code, infections stood at about 91 per 10,000 residents — about 2.5 times more prevalent than the average statewide.

No. 8: 97701 — Bend

This ZIP code covers a large swath of northern Bend and areas to the east and west. Cases here more than doubled — growing by 42, to a total of 112.

Overall, the per capita rate of cases in 97701 is relatively low, about 28 per 10,000 residents have been infected — below the statewide average of about 37.

No. 9: 97230 — Northeast Portland

Cases here rose by 41, to 254 total cases. The per capita rate of cases was 63 per 10,000 residents, about 1.7 times the statewide rate.

No. 10: 97882 — Umatilla

This northeastern ZIP code, just south of the Oregon-Washington border, saw 40 new cases — with cases climbing from 163 to 203. That’s a 25% jump.

The Oregon Health Authority reported a new outbreak this month at the plastic pipe manufacturer, JM Eagle in Umatilla, with 10 cases. The per capita rate of infections in 97882 is 250 per 10,000 residents — that’s more than six times the statewide average.