It was a rough summer for Chipotle Mexican Grill (NYSE:CMG), as a July norovirus outbreak at a Virginia restaurant sent the stock reeling. Then an all-natural queso was released in several test markets before being rolled out nationwide in mid-September, causing some to swoon, but also sparking mockery.

Now it's fall and Chipotle is set to report third-quarter results on Oct. 24. There are several moving parts to this report and here's what investors should look for.

Two pairs of arms and hands playing tug-of-war with a rope

Image source: Getty Images.

A different way to look at things

As always, analysts will be on the lookout for comparable-store sales, which track how much the average restaurant earned compared with last year. Obviously, only restaurants that are at least a year old qualify for the calculation.

The norovirus incident may well have put a crimp in Chipotle's sales in the quarter, although perhaps the late-quarter rollout of queso could offset the blemish. On the last earnings call, on July 25, Chipotle management said the outbreak had decreased same-store sales by 5.5% over the past several days.

Since we're now two years removed from the infamous 2015 E. coli incident, investors may wish to look at the "two-year stack," or comparable-store traffic compared with two years ago (pre-E.coli).

Here's how that two-year stack looks over the past three quarters:

Period Two-Year Stack
Q4 (18.7%)
Q1 (17.2%) 
Q2 (17.4%) 

Data source: Chipotle. Calculation by author.

As you can see, the "stack" ain't pretty. Though the metric showed marked improvement in the first quarter, it dropped back again in Q2 and is still well below 2015 levels. This could have been due to the data breach announced on the first-quarter earnings call, or merely be a bump on the way to an uneven recovery. Still, things weren't exactly going great, even before the July norovirus incident.

Can queso save?

There's been a lot of hype about this summer's queso rollout, which did seem to overwhelm the news around the norovirus incident. But at least one analyst, Andrew Charles of Cowen, whose note was quoted by CNBC, was skeptical:

In our prior analysis we saw the Week 1 queso lift progressively decelerate through Week 2. This trend of a deteriorating lift from queso intensified through Week 3 to end 3Q. ... We view the data as supportive in our belief that queso is unlikely to be a sustainable driver of sales.

Chipotle reacted fairly strongly to Charles' commentary, as well as to the ongoing narrative (on social media, at least) that people don't like Chipotle's queso. Company spokesperson Chris Arnold released a statement saying:

... we moved queso from marketwide testing to a national rollout because we were encouraged by the results, both in terms of feedback in consumer research and sales ... What we have seen in terms of brand health and consumer sentiment is quite different than what the Cowen report suggests. ... Rather than providing a look at any single moment in time, that research provides an indication of where consumer sentiment stands on an ongoing basis. What we are seeing there is that we are closer to the levels we were seeing in early or mid-2015 (pre-crisis) than we are to the troughs, with many metrics at or near pre-crisis levels.

That may be true, but if Chipotle's internal research is showing sentiment is back to mid-2015 levels, it hasn't led to mid-2015 least not yet.

Look for fourth-quarter commentary

Chipotle shareholders shouldn't exactly panic, however. Consider what happened when took over Whole Foods in August and promptly cut prices: Initial research showed a huge increase in interest when the cuts were introduced, but then a deceleration over the next two weeks. Three weeks later, Whole Foods had retained a mid-single-digit increase in year-over-year traffic. In other words, I think it's inevitable that traffic decelerates after the immediate spike when a hyped product is unveiled.

On Chipotle's earnings calls, management usually comments on traffic trends for the first three weeks of the current quarter, so that -- not this war of words -- is where investors should focus.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.