What should a Christian do if they've contracted a sexually transmitted disease (STD)?

TL;DR:

Christians who contracted an STD as a result of sin should repent of the sin and ask God for forgiveness. Those who contracted STDs because of a spouse’s sin should offer forgiveness, seek counseling from a trusted Christian, and know that God works all things, even painful circumstances, for good to those who love Him.

what does the bible say?

The Bible doesn’t mention any sexually transmitted diseases (STDs) by name, but it speaks against sexual immorality (1 Thessalonians 4:3, Colossians 3:5, Hebrews 13:4), which is the cause of STDs. God’s created order was for sex to be between one man and one woman in the context of marriage (Genesis 2:24). Straying from that concept is sinful and results in hurt and suffering (Genesis 3:17; Romans 5:12); STDs are an example of that. Such diseases originate in someone’s sexual immorality—either the person with the disease or the one who passed it on to him or her. The Bible teaches the concept of sowing and reaping (Galatians 6:7), and Christians often have to deal with the present consequences of their past sins even after they’ve come to Christ. But the consequences of sexual sin are no worse, spiritually, than the consequences of other sins. All believers can take comfort in God’s mercy and promise of forgiveness when we repent (1 John 1:9). Scripture also promises believers that God works “all things” (emphasis added) for our good, even circumstances that we may think nothing good can come out of (Romans 8:28).

from the old testament

God’s created order was for sex to be between one man and one woman in the context of marriage (Genesis 2:24). When people stray from that, harmful consequences like STDs occur.
Even if we have an STD because of our sin, our gracious heavenly Father offers us forgiveness. David, a man who sinned egregiously yet loved the Lord, wrote, “I acknowledged my sin to you, and I did not cover my iniquity; I said, ‘I will confess my transgressions to the Lord,’ and you forgave the iniquity of my sin” (Psalm 32:5). Like David, we are “Blessed” to have a merciful God who forgives our sins (Psalm 32:1-2).

from the new testament

Jesus reaffirmed that sex and any associated behavior should be confined to a marriage between one man and one woman (Matthew 19:4-6). The practical effect of adhering to that order is protection against such consequences as STDs.
STDs are a result of sexual immorality—whether from a past sinful lifestyle, a current lapse into sin, or the sin of a spouse. Sexual immorality has no place in the life of a Christian (1 Thessalonians 4:3, Colossians 3:5, Hebrews 13:4). But if we fall into sin, we can confess our sins to God, and He has promised forgiveness (1 John 1:9).
We become new creations in Christ (2 Corinthians 5:17), but sometimes we must live with the consequences of the sins from our old life (Galatians 6:7). STDs may be one of those consequences.
Even if we have an STD from our past sinful lifestyle or the sin of our spouse, we can take comfort in the promise of Romans 8:28: “And we know that for those who love God all things work together for good, for those who are called according to his purpose.” God can use any circumstance in our life for our good and His glory.

implications for today

People like catching things. Someone might run to catch a bus. A baseball player might jump to catch a flyball. Two young people might be said to “catch” feelings for each other. But no one wants to catch a disease. Yet many people do, and sometimes, they do it through sexual activity that should have been reserved for marriage.

In this era of “swiping right” to signal interest in someone, waiting until marriage for sex seems as antiquated as taking a horse and buggy to work. But God’s way is timeless, and He designed sex to be between one man and one woman for one lifetime within the context of marriage (Genesis 2:24). Following God’s way rather than the world’s way demonstrates our trust and love for Him. And it has the practical implication of protecting us from harmful consequences like sexually transmitted diseases.

Even if you’re living with the results of past sin, know that God offers forgiveness and will work even the harmful results of your sin into good for you (Romans 8:28).

understand

The Bible doesn’t mention any sexually transmitted diseases (STDs) by name, but it speaks against sexual immorality.
God’s created order was for sex to be between one man and one woman in the context of marriage.
Even if a person or spouse strays from the created order there is grace and forgiveness in Christ.

reflect

If you have contracted an STD, how have you repented and made yourself right with the Lord?
If your spouse has sinned and you now have an STD, how have you dealt with forgiveness and reconciliation?
How can you encourage a friend or family member to avoid STDs by staying pure?

engage

How might we engage with friends who are living selfish, sinful lives?
When should we confront a friend who lives a sexually sinful lifestyle?
How can we share the forgiveness of the Gospel with those who are dealing with STDs?