The phrase "a couple cases" is correct and usable in written English.
It can be used when referring to a small number of instances or examples, typically two or three.
Example: "In a couple cases, the results were not as expected, leading us to reevaluate our approach."
Alternatives: "a few cases" or "several cases".
"It started with just a couple cases like that, but they kept multiplying," Sheriff Dart said.
"Some teams are comfortable with not only having cheerleaders but selling cheerleader swimsuit calendars or in a couple cases lingerie calendars.
If, in any given year, they just go to the doctor for a few regular check-ups, and maybe a couple cases of strep throat, then the gamble pays off.
But it is not clear how active each office is, and in a couple cases the number of offices reported by the Obama campaign differs from the number reported in news accounts, although by just a few offices.
(In fairness, they have in a couple cases found genuinely new material, like a panel about Saul Alinsky that Obama participated in, and a brochure put out by his former literary agent that mistakenly places his birth in Kenya, but those are interesting curiosities and not much more).
This is great for grabbing a couple cases of wine and a pile of groceries.
"You have one case or a couple of cases, well, that happens.
Mr. Schott said the I.R.S. had looked "at a couple of cases and discovered some issues, and we're expanding this to look at other cases".
We investigated a couple of cases with different output functions, showing that the type of function is of great importance.
In most of those cases, local bloggers, reporters and lawyers have traced connections to local Democrats, drawing lawsuits, complaints and, in a couple of cases, admissions of involvement.
