Hvis der er meget smitte på kontoret, bliver flere kolleger hjemme.

Because Danish uses verb-second word order in main clauses.

The sentence starts with a subordinate clause:

Hvis der er meget smitte på kontoret
= If there is a lot of contagion/infection in the office

After that clause, the main clause begins, and in a Danish main clause, the finite verb normally comes in second position. So you get:

..., bliver flere kolleger hjemme.

Not:

..., flere kolleger bliver hjemme.

That would sound wrong in standard Danish after a fronted clause.

Here, der works like English there in there is / there are.

So:

der er meget smitte
literally: there is much infection/contagion

It does not mean there as in a physical place. It is an existential der, used to introduce the existence or presence of something.

Very common pattern:

• Der er en bog på bordet. = There is a book on the table.
• Der er mange mennesker her. = There are many people here.

Because smitte here is treated as an uncountable noun.

So Danish uses:

• meget with uncountable nouns
• mange with countable plural nouns

Compare:

• meget smitte = a lot of infection/contagion
• mange kolleger = many colleagues

You normally would not say smitter here, because the idea is not separate infections, but infection/spread of disease in general.

Smitte is a noun meaning something like:

• infection
• contagion
• spread of disease

In this sentence, it refers to there being a lot of contagious illness going around in the office.

It is a somewhat general word, so the best English translation depends on context. In workplace or health-related contexts, it often means a lot of transmission/infection is going around.

In Danish, på is often used for workplaces, institutions, and similar settings where English might use in or at.

So:

• på kontoret = at/in the office
• på skolen = at school
• på hospitalet = at the hospital

I kontoret would usually sound less natural here. Danish prefers på kontoret when talking about the office as a workplace environment.

Yes, blive often means become, but it also has other common uses.

In the expression blive hjemme, it means:

• stay home
• remain at home

So:

flere kolleger bliver hjemme
= more colleagues stay home

This is a fixed and very common expression. You should learn blive hjemme as a phrase.

Because flere kolleger means more colleagues or several colleagues, and that phrase is already indefinite.

Danish does not need an article here.

Compare:

• en kollega = a colleague
• kollegaen = the colleague
• flere kolleger = more colleagues / several colleagues

So flere already functions as the determiner.

It can suggest either, depending on context.

Most literally, flere means more. But in real usage it can also feel like several if the comparison is only implied.

So this sentence could mean:

• more colleagues stay home or
• several colleagues stay home

If the wider context already involves comparison with a normal situation, more colleagues is a natural reading.

The comma separates the subordinate clause from the main clause.

Here:

Hvis der er meget smitte på kontoret, bliver flere kolleger hjemme.

The hvis clause comes first, so Danish writes a comma before the main clause begins.

This is standard Danish punctuation.

Not in all cases, but here it matches English if very well.

Hvis is used for conditions:

• Hvis det regner, bliver vi hjemme.
  = If it rains, we stay home.

But English if can also mean whether. In Danish, that is often om, not hvis.

Compare:

• Jeg ved ikke, om han kommer. = I don't know if/whether he is coming.
• Hvis han kommer, bliver jeg glad. = If he comes, I’ll be happy.

So in your sentence, hvis is the correct conditional word.

Yes.

You could say:

Flere kolleger bliver hjemme, hvis der er meget smitte på kontoret.

That is also correct.

The difference is mainly about focus and style:

• Starting with Hvis ... emphasizes the condition first.
• Starting with Flere kolleger ... emphasizes the result first.

When the hvis clause comes first, the main clause must still follow the verb-second rule:

Hvis ..., bliver flere kolleger hjemme.

Kontoret is the definite form: the office.

Danish adds the definite article to the end of the noun:

• et kontor = an office
• kontoret = the office

In this sentence, the speaker is talking about a specific office that both speaker and listener understand from context, so the definite form is natural.

Normally, no—not in this kind of sentence.

When smitte means infection/contagion in a general sense, it is usually used as an uncountable mass noun, so you say:

• meget smitte
• lidt smitte
• ingen smitte

Using en smitte would usually not fit this meaning.

It can be understood as a general tendency or policy.

The present tense in Danish is often used for general truths, habits, or regular outcomes:

Hvis der er meget smitte på kontoret, bliver flere kolleger hjemme.

This can mean something like:

• whenever that situation happens, this is what usually happens

So it does not have to refer to one specific moment only.

A very literal translation would be something like:

If there is much contagion at the office, become more colleagues home.

That sounds wrong in English, which shows why it is better to understand the Danish structure on its own terms:

• der er = there is
• meget smitte = a lot of infection/contagion
• bliver hjemme = stay home

So even though the sentence is easy to understand, some parts should be learned as Danish patterns rather than translated word for word.