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Nearly 50% Of Covid Tests Analyzed In Los Angeles Are Now More Infectious Delta Variant

·6-min read

“We are starting to see small increases in daily hospitalizations, cases and deaths,” said Los Angeles Public Health Director Barbara Ferrer. She called the rising numbers “a warning.”

On Thursday, 314 new Covid-19 cases were reported in L.A. That is the largest daily number of new cases in the county since May 15. The rise in identified cases has come despite a plummeting demand for tests, from a weekly average of about 65,000 in early June to about 40,000 last week.

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The county’s 7-day test positivity rate, which Ferrer called one of the most reliable measures of infection spread, has also risen over roughly the past two weeks. L.A. bottomed out most recently in early June at just above 0.4%. On Thursday, Ferrer reported it at 0.74%, a near doubling in two weeks.

<img src="; alt=" - Credit: LADPH" width="1024" height="709" class="size-large wp-image-1234781272" srcset=" 1562w,,104 150w,,208 300w,,709 1024w,,1064 1536w,,42 60w,,244 352w,,76 110w,,197 285w,,222 320w,,443 640w,,554 800w,,887 1280w" sizes="(max-width: 1024px) 100vw, 1024px" />LADPH

Also concerning is the prevalence of the more infectious Delta (and related Kappa) variants, which have overrun much of India and the U.K. Ferrer announced on Thursday that currently “nearly 48% of all samples sequenced” were related to Delta.” The total was 124 cases. Between late April and early June, just 64 cases of Delta-related infections were identified among residents of Los Angeles County. That would indicate a rapidly increasing prevalence of the variant.

<img src="; alt=" - Credit: L.A. County Public Health" width="1024" height="581" class="size-large wp-image-1234781229" srcset=" 1762w,,85 150w,,170 300w,,581 1024w,,872 1536w,,70 125w,,112 200w,,152 270w,,34 60w,,200 352w,,62 110w,,162 285w,,182 320w,,363 640w,,454 800w,,726 1280w" sizes="(max-width: 1024px) 100vw, 1024px" />L.A. County Public Health

Ferrer cautioned however, “It’s important not to generalize from this data to the general population.” She noted that the 48% number was not of the total Covid tests count, but merely those flagged as suspicious and then given the much more expensive genomic sequencing that determines the causal variant. She said that there had been 6,732 specimens genomically sequenced, though it was unclear whether that was a pandemic total or just in the past week. Given the rarity of such sequencing, it is likely the former.

Data shows that half of the Delta cases are outbreak related. Many of them are geographically clustered, with many of them centered in the Palmdale and Lancaster area – 43 of the 123 cases identified as Delta. Fourteen instances of the variant were traced to just one household, said Ferrer.

California reported on Thursday that, since May 21, the percentage of Delta variants found in samples genomically sequenced statewide had grown from 5% to about 15%. That’s a tripling in four weeks.

Nationwide, the CDC estimates the Delta variant accounted for about 10% of new cases in the U.S. last week. On May 22, the variant made up only 2.7% of new cases, according to the CDC. This past week, that percentage rose to 20%.

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