Sweetgreen stock plunged 15% in Thursday's afterhours trading, even though the salad chain posted second-quarter results that showed signs that its turnaround was gaining traction.

A sharp cut to the company's 2026 outlook could be the main driver behind the stock's tumble, as it warned that nationwide food-safety scare could lead to weakening demand at salad-focused restaurants.

Sweetgreen shares already fell sharply when a food-borne illness outbreak was first publicized on July 14 involving certain types of lettuce, and lost 27% during the month. Shares declined 3.85% to $5.87 Thursday before the earnings release.

For the quarter ended in June, revenue rose 3.8% from a year earlier to $192.7 million, but came slightly below the $194.5 million expectated by analysts polled by FactSet.

Much of the sales growth came from new store openings. Sweetgreen's same-store sales actually fell 6.2%, thanks to a 2% decrease in foot traffic and a 4.2% headwind in average ticket size due to heavier promotions and customers choosing lower-priced products.

Profitability remained under pressure. The salad chain lost 22 cents a share during the quarter, two cents more than the year-ago period and more than Wall Street's expectation for a 15 cents loss.

Restaurant-level margin contracted by nearly six percentage points to 13.1%, hurt by weaker comparable sales, higher ingredient usage, larger chicken and tofu portions, and promotions, according to the company.

The more consequential news was Sweetgreen's sharply reduced full-year outlook. Management said demand for fresh prepared foods has weakened since mid-July because of the multistate cyclosporiasis outbreak.

Sweetgreen now expects same-store sales to fall 7% to 8% for fiscal 2026, versus its previous forecast for a 2% to 4% decline. It projects a restaurant-level margin of 10.5% to 11%, down from 14.2% to 14.7%.

Adjusted earnings before interest, taxes, depreciation, and amortization are expected to come at a loss of $23 million to $27 million, compared with its prior expectation for a $1 million to $6 million profit.

Sweetgreen has said it does not use iceberg lettuce -- the product identified in the federal investigation -- and that none of its ingredients had been linked to the cyclosporiasis outbreak.

The gloomier outlook is especially painful because things had been improving before the outbreak. Although same-store sales remained lower than a year ago in the June quarter, the trends improved from a 12.8% decline in the previous three months.

Placer.ai estimated that same-store visits rose 1% in May and 3.9% in June, partially thanks to Sweetgreen's nationwide wrap launch. The firm found that traffic at Sweetgreen weakened for just a week after the outbreak became public, but has recovered since then.

Investors now must assess whether the sales shock fades quickly or continues to disrupt Sweetgreen's fragile turnaround as the broader consumer remains anxious over fresh produce.