The result is in and it's positive. While you're still working out what it means for you, the next thought has already pushed its way in: who needs to know about this?

This is where a lot of people get stuck, because the result itself often causes less of a headache than the messages that come with it. The chat with the person from last month, the ex you haven't written to in weeks, plus the match whose surname you never learned.

What follows won't write the message for you, but it will sort out who to tell, how much time you have, which channel works best and what to say when the words won't come.

Why the message is worth more than it costs

Most STIs show no symptoms at all, so no itching, no burning, no discharge and nothing that would prompt anyone to go and get tested on their own. That's precisely what makes them so good at being passed on, because without your message an infection stays undetected in the other person and carries on travelling at its leisure.

Then there's the ping-pong effect, which catches more people than you'd think: you get treated, you're fine two weeks later and the next time you sleep with the same person you pick it straight back up, because treatment only does its job when it reaches everyone involved.

Left alone, an infection like this rarely stays harmless either. Chlamydia and gonorrhoea can move up the reproductive tract and affect fertility, while syphilis runs on for years and eventually reaches the nerves, heart or blood vessels. A message that costs you five minutes of nerve can therefore spare someone else a great deal.

Who to tell

The real question is how far back you need to go. That depends on the infection. The windows below follow the recommendations of BASHH, the British sexual health association whose guidance is used as a reference internationally:

• Chlamydia: everyone from the past six months, although with symptoms in the penis the four weeks before symptoms started are enough.
• Gonorrhoea: the past three months, or with symptoms in the penis the two weeks before they started.
• Trichomonas: the past four weeks.
• Syphilis: highly dependent on the stage, three months in early infection and sometimes two years or more later on, which is why your clinician sets the window here.
• HIV: from the estimated point of infection plus the three months before it.

Two notes on that. These are guide values. The window that applies to you gets worked out at the clinic or at a sexual health service. And when in doubt you're better off telling one person too many than one too few, because an unnecessary test harms nobody while a missed infection certainly can.

All of this covers every contact where transmission was possible, which includes oral sex and one-night stands.

How fast it needs to happen

Promptly, although you're still allowed to take a breath first. A day or two to digest the result yourself is entirely reasonable, since waiting beyond that only makes it harder without making the message any easier.

The pace has a practical reason behind it: the sooner the other person gets tested and treated, the shorter the chain behind them stays. On top of that come the protective options that only work right after the exposure. HIV emergency prophylaxis has to start within 72 hours of the risk contact and works more reliably the earlier it begins. Antibiotic PEP against bacterial STIs has the same 72-hour window, with the same rule that earlier is better. Both are prescription-only and reviewed by a clinician first, because the same thing isn't recommended for everyone. So if the contact was very recent, hours genuinely count.

Which channel to use

No channel is inherently more correct than the others, there are just some that fit a given relationship better than others.

In person or on the phone is where the message belongs if you're together or close, because anything else in that kind of setup quickly reads as dodging.

A message is entirely legitimate for everyone else and often the kinder option, because the other person can then react whenever they want, doesn't have to produce a feeling in front of you and can read the whole thing in their own time. Write on whichever channel you met on, which for app contacts means the app's own chat.

Anonymously works too. Germany has no nationwide system for it so far, although individual sexual health centres and public health offices do offer anonymous notification. At Every Health it's built in: after a positive result from Reality Check you can have your sexual contacts notified anonymously. They find out that a test would be worth doing without your name appearing anywhere.

What you shouldn't do along the way: justify yourself, lay out your testing history or answer the question of who you got it from. That one usually can't be answered anyway.

Three messages you can just copy

If the words won't come, take one of these and change anything that doesn't fit.

In a relationship:

There's something I need to tell you and I'd rather write it before we see each other tonight. My test came back positive for XX, which means you should get tested too. Let's talk properly when you're here.

Someone you haven't been in touch with for a while:

Hey, awkward message, but you should know: I've tested positive for XX and it could be from our time together. Please get tested even if you feel completely fine, because most people do. It's very treatable.

An app contact:

Hi, we had sex a few weeks ago. I've just tested positive for XX and I'm letting everyone know who might be affected. There are often no symptoms at all, so a test makes sense. No drama from my side, I just wanted you to know.

Short, factual and without much ceremony is genuinely enough here, since anything else will come up in the conversation anyway.

What might come back

The most common reaction, by the way, is a thank you, which is what the fewest people expect.

Other things can obviously come back too, from panic to blame to a small interrogation about who else you've slept with. Sometimes nothing comes back at all. Silence feels awful, but it usually just means someone needs a few hours to make sense of it.

You're not responsible for the reaction, your job was the information and the other person works out the rest for themselves. The question of blame gets nobody anywhere either, because with most STIs it simply can't be answered: incubation periods overlap and infections stay silent for months.

If you're afraid of the reaction because violence has been part of the relationship, take the anonymous route or talk to a support service first. Looking after yourself takes priority over everything else in that situation.

Where you stand legally

You don't have to report anyone or anything yourself. Once a result has been confirmed in the lab, HIV and syphilis go to the Robert Koch Institute as a non-identifying notification in which your name never appears. A home test like Reality Check doesn't trigger that notification, because a reactive screening result always gets clarified by a second, confirmatory test first. There's no legal obligation in Germany to inform partners either.

With HIV there's one more thing worth knowing, namely that treatment taken reliably pushes the viral load below the limit of detection, at which point HIV can no longer be passed on, condom or not. If you have legal questions around an HIV diagnosis, the Aidshilfe organisations advise on exactly that, free of charge and anonymously if you prefer.

What happens next

Both of you get treated. Bacterial STIs are usually straightforward to treat. All that matters is that everyone involved actually gets their treatment, because otherwise the ping-pong starts all over again.

Take a break from sex until treatment is finished for both of you and any symptoms have gone. Your clinician will tell you how long that takes in your case.

Test for the rest too. A second infection can be running alongside unnoticed, mostly because so many STIs come without symptoms, which is why guidelines recommend testing for the other relevant pathogens once one result comes back positive, everywhere you have sex. Reality Check covers that from home, the lab result is usually back around 24 hours after your samples arrive and if chlamydia comes back positive you can get the treatment straight through Every Health.

Don't skip the follow-up test. With some infections there's a check afterwards to confirm everything has actually cleared, which is best planned together with your practice.

Set yourself up for next time. Testing regularly achieves a lot more than waiting for something to feel off.

The message takes two minutes

The worst part of this message is the half hour before it, the one where you've already written and deleted it twenty times in your head. The typing itself is quick, the answer usually comes back friendlier than you feared and afterwards you've done something the other person couldn't have managed alone, simply because they were missing the information.

An STI says nothing about how you treat people. How you handle a diagnosis says rather a lot.